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• How to Write a Literature Review | Guide, Examples, & Templates

How to Write a Literature Review | Guide, Examples, & Templates

Published on January 2, 2023 by Shona McCombes . Revised on September 11, 2023.

What is a literature review? A literature review is a survey of scholarly sources on a specific topic. It provides an overview of current knowledge, allowing you to identify relevant theories, methods, and gaps in the existing research that you can later apply to your paper, thesis, or dissertation topic .

There are five key steps to writing a literature review:

• Search for relevant literature
• Evaluate sources
• Identify themes, debates, and gaps
• Outline the structure
• Write your literature review

A good literature review doesn’t just summarize sources—it analyzes, synthesizes , and critically evaluates to give a clear picture of the state of knowledge on the subject.

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Table of contents

What is the purpose of a literature review, examples of literature reviews, step 1 – search for relevant literature, step 2 – evaluate and select sources, step 3 – identify themes, debates, and gaps, step 4 – outline your literature review’s structure, step 5 – write your literature review, free lecture slides, other interesting articles, frequently asked questions, introduction.

• Quick Run-through
• Step 1 & 2

When you write a thesis , dissertation , or research paper , you will likely have to conduct a literature review to situate your research within existing knowledge. The literature review gives you a chance to:

• Demonstrate your familiarity with the topic and its scholarly context
• Develop a theoretical framework and methodology for your research
• Position your work in relation to other researchers and theorists
• Show how your research addresses a gap or contributes to a debate
• Evaluate the current state of research and demonstrate your knowledge of the scholarly debates around your topic.

Writing literature reviews is a particularly important skill if you want to apply for graduate school or pursue a career in research. We’ve written a step-by-step guide that you can follow below.

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Writing literature reviews can be quite challenging! A good starting point could be to look at some examples, depending on what kind of literature review you’d like to write.

• Example literature review #1: “Why Do People Migrate? A Review of the Theoretical Literature” ( Theoretical literature review about the development of economic migration theory from the 1950s to today.)
• Example literature review #2: “Literature review as a research methodology: An overview and guidelines” ( Methodological literature review about interdisciplinary knowledge acquisition and production.)
• Example literature review #3: “The Use of Technology in English Language Learning: A Literature Review” ( Thematic literature review about the effects of technology on language acquisition.)
• Example literature review #4: “Learners’ Listening Comprehension Difficulties in English Language Learning: A Literature Review” ( Chronological literature review about how the concept of listening skills has changed over time.)

You can also check out our templates with literature review examples and sample outlines at the links below.

Download Word doc Download Google doc

Before you begin searching for literature, you need a clearly defined topic .

If you are writing the literature review section of a dissertation or research paper, you will search for literature related to your research problem and questions .

Make a list of keywords

Start by creating a list of keywords related to your research question. Include each of the key concepts or variables you’re interested in, and list any synonyms and related terms. You can add to this list as you discover new keywords in the process of your literature search.

• Social media, Facebook, Instagram, Twitter, Snapchat, TikTok
• Body image, self-perception, self-esteem, mental health
• Generation Z, teenagers, adolescents, youth

Search for relevant sources

Use your keywords to begin searching for sources. Some useful databases to search for journals and articles include:

• Your university’s library catalogue
• Google Scholar
• Project Muse (humanities and social sciences)
• Medline (life sciences and biomedicine)
• EconLit (economics)
• Inspec (physics, engineering and computer science)

You can also use boolean operators to help narrow down your search.

Make sure to read the abstract to find out whether an article is relevant to your question. When you find a useful book or article, you can check the bibliography to find other relevant sources.

You likely won’t be able to read absolutely everything that has been written on your topic, so it will be necessary to evaluate which sources are most relevant to your research question.

For each publication, ask yourself:

• What question or problem is the author addressing?
• What are the key concepts and how are they defined?
• What are the key theories, models, and methods?
• Does the research use established frameworks or take an innovative approach?
• What are the results and conclusions of the study?
• How does the publication relate to other literature in the field? Does it confirm, add to, or challenge established knowledge?
• What are the strengths and weaknesses of the research?

Make sure the sources you use are credible , and make sure you read any landmark studies and major theories in your field of research.

You can use our template to summarize and evaluate sources you’re thinking about using. Click on either button below to download.

Take notes and cite your sources

As you read, you should also begin the writing process. Take notes that you can later incorporate into the text of your literature review.

It is important to keep track of your sources with citations to avoid plagiarism . It can be helpful to make an annotated bibliography , where you compile full citation information and write a paragraph of summary and analysis for each source. This helps you remember what you read and saves time later in the process.

To begin organizing your literature review’s argument and structure, be sure you understand the connections and relationships between the sources you’ve read. Based on your reading and notes, you can look for:

• Trends and patterns (in theory, method or results): do certain approaches become more or less popular over time?
• Themes: what questions or concepts recur across the literature?
• Debates, conflicts and contradictions: where do sources disagree?
• Pivotal publications: are there any influential theories or studies that changed the direction of the field?
• Gaps: what is missing from the literature? Are there weaknesses that need to be addressed?

This step will help you work out the structure of your literature review and (if applicable) show how your own research will contribute to existing knowledge.

• Most research has focused on young women.
• There is an increasing interest in the visual aspects of social media.
• But there is still a lack of robust research on highly visual platforms like Instagram and Snapchat—this is a gap that you could address in your own research.

There are various approaches to organizing the body of a literature review. Depending on the length of your literature review, you can combine several of these strategies (for example, your overall structure might be thematic, but each theme is discussed chronologically).

Chronological

The simplest approach is to trace the development of the topic over time. However, if you choose this strategy, be careful to avoid simply listing and summarizing sources in order.

Try to analyze patterns, turning points and key debates that have shaped the direction of the field. Give your interpretation of how and why certain developments occurred.

If you have found some recurring central themes, you can organize your literature review into subsections that address different aspects of the topic.

For example, if you are reviewing literature about inequalities in migrant health outcomes, key themes might include healthcare policy, language barriers, cultural attitudes, legal status, and economic access.

Methodological

If you draw your sources from different disciplines or fields that use a variety of research methods , you might want to compare the results and conclusions that emerge from different approaches. For example:

• Look at what results have emerged in qualitative versus quantitative research
• Discuss how the topic has been approached by empirical versus theoretical scholarship
• Divide the literature into sociological, historical, and cultural sources

Theoretical

A literature review is often the foundation for a theoretical framework . You can use it to discuss various theories, models, and definitions of key concepts.

You might argue for the relevance of a specific theoretical approach, or combine various theoretical concepts to create a framework for your research.

Like any other academic text , your literature review should have an introduction , a main body, and a conclusion . What you include in each depends on the objective of your literature review.

The introduction should clearly establish the focus and purpose of the literature review.

Depending on the length of your literature review, you might want to divide the body into subsections. You can use a subheading for each theme, time period, or methodological approach.

As you write, you can follow these tips:

• Summarize and synthesize: give an overview of the main points of each source and combine them into a coherent whole
• Analyze and interpret: don’t just paraphrase other researchers — add your own interpretations where possible, discussing the significance of findings in relation to the literature as a whole
• Critically evaluate: mention the strengths and weaknesses of your sources
• Write in well-structured paragraphs: use transition words and topic sentences to draw connections, comparisons and contrasts

In the conclusion, you should summarize the key findings you have taken from the literature and emphasize their significance.

When you’ve finished writing and revising your literature review, don’t forget to proofread thoroughly before submitting. Not a language expert? Check out Scribbr’s professional proofreading services !

This article has been adapted into lecture slides that you can use to teach your students about writing a literature review.

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If you want to know more about the research process , methodology , research bias , or statistics , make sure to check out some of our other articles with explanations and examples.

• Sampling methods
• Simple random sampling
• Stratified sampling
• Cluster sampling
• Likert scales
• Reproducibility

 Statistics

• Null hypothesis
• Statistical power
• Probability distribution
• Effect size
• Poisson distribution

Research bias

• Optimism bias
• Cognitive bias
• Implicit bias
• Hawthorne effect
• Anchoring bias
• Explicit bias

A literature review is a survey of scholarly sources (such as books, journal articles, and theses) related to a specific topic or research question .

It is often written as part of a thesis, dissertation , or research paper , in order to situate your work in relation to existing knowledge.

There are several reasons to conduct a literature review at the beginning of a research project:

• To familiarize yourself with the current state of knowledge on your topic
• To ensure that you’re not just repeating what others have already done
• To identify gaps in knowledge and unresolved problems that your research can address
• To develop your theoretical framework and methodology
• To provide an overview of the key findings and debates on the topic

Writing the literature review shows your reader how your work relates to existing research and what new insights it will contribute.

The literature review usually comes near the beginning of your thesis or dissertation . After the introduction , it grounds your research in a scholarly field and leads directly to your theoretical framework or methodology .

A literature review is a survey of credible sources on a topic, often used in dissertations , theses, and research papers . Literature reviews give an overview of knowledge on a subject, helping you identify relevant theories and methods, as well as gaps in existing research. Literature reviews are set up similarly to other  academic texts , with an introduction , a main body, and a conclusion .

An  annotated bibliography is a list of  source references that has a short description (called an annotation ) for each of the sources. It is often assigned as part of the research process for a  paper .  

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Writing a Literature Review

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A literature review is a document or section of a document that collects key sources on a topic and discusses those sources in conversation with each other (also called synthesis ). The lit review is an important genre in many disciplines, not just literature (i.e., the study of works of literature such as novels and plays). When we say “literature review” or refer to “the literature,” we are talking about the research ( scholarship ) in a given field. You will often see the terms “the research,” “the scholarship,” and “the literature” used mostly interchangeably.

Where, when, and why would I write a lit review?

There are a number of different situations where you might write a literature review, each with slightly different expectations; different disciplines, too, have field-specific expectations for what a literature review is and does. For instance, in the humanities, authors might include more overt argumentation and interpretation of source material in their literature reviews, whereas in the sciences, authors are more likely to report study designs and results in their literature reviews; these differences reflect these disciplines’ purposes and conventions in scholarship. You should always look at examples from your own discipline and talk to professors or mentors in your field to be sure you understand your discipline’s conventions, for literature reviews as well as for any other genre.

A literature review can be a part of a research paper or scholarly article, usually falling after the introduction and before the research methods sections. In these cases, the lit review just needs to cover scholarship that is important to the issue you are writing about; sometimes it will also cover key sources that informed your research methodology.

Lit reviews can also be standalone pieces, either as assignments in a class or as publications. In a class, a lit review may be assigned to help students familiarize themselves with a topic and with scholarship in their field, get an idea of the other researchers working on the topic they’re interested in, find gaps in existing research in order to propose new projects, and/or develop a theoretical framework and methodology for later research. As a publication, a lit review usually is meant to help make other scholars’ lives easier by collecting and summarizing, synthesizing, and analyzing existing research on a topic. This can be especially helpful for students or scholars getting into a new research area, or for directing an entire community of scholars toward questions that have not yet been answered.

What are the parts of a lit review?

Most lit reviews use a basic introduction-body-conclusion structure; if your lit review is part of a larger paper, the introduction and conclusion pieces may be just a few sentences while you focus most of your attention on the body. If your lit review is a standalone piece, the introduction and conclusion take up more space and give you a place to discuss your goals, research methods, and conclusions separately from where you discuss the literature itself.

Introduction:

• An introductory paragraph that explains what your working topic and thesis is
• A forecast of key topics or texts that will appear in the review
• Potentially, a description of how you found sources and how you analyzed them for inclusion and discussion in the review (more often found in published, standalone literature reviews than in lit review sections in an article or research paper)
• Summarize and synthesize: Give an overview of the main points of each source and combine them into a coherent whole
• Analyze and interpret: Don’t just paraphrase other researchers – add your own interpretations where possible, discussing the significance of findings in relation to the literature as a whole
• Critically Evaluate: Mention the strengths and weaknesses of your sources
• Write in well-structured paragraphs: Use transition words and topic sentence to draw connections, comparisons, and contrasts.

Conclusion:

• Summarize the key findings you have taken from the literature and emphasize their significance
• Connect it back to your primary research question

How should I organize my lit review?

Lit reviews can take many different organizational patterns depending on what you are trying to accomplish with the review. Here are some examples:

• Chronological : The simplest approach is to trace the development of the topic over time, which helps familiarize the audience with the topic (for instance if you are introducing something that is not commonly known in your field). If you choose this strategy, be careful to avoid simply listing and summarizing sources in order. Try to analyze the patterns, turning points, and key debates that have shaped the direction of the field. Give your interpretation of how and why certain developments occurred (as mentioned previously, this may not be appropriate in your discipline — check with a teacher or mentor if you’re unsure).
• Thematic : If you have found some recurring central themes that you will continue working with throughout your piece, you can organize your literature review into subsections that address different aspects of the topic. For example, if you are reviewing literature about women and religion, key themes can include the role of women in churches and the religious attitude towards women.
• Qualitative versus quantitative research
• Empirical versus theoretical scholarship
• Divide the research by sociological, historical, or cultural sources
• Theoretical : In many humanities articles, the literature review is the foundation for the theoretical framework. You can use it to discuss various theories, models, and definitions of key concepts. You can argue for the relevance of a specific theoretical approach or combine various theorical concepts to create a framework for your research.

What are some strategies or tips I can use while writing my lit review?

Any lit review is only as good as the research it discusses; make sure your sources are well-chosen and your research is thorough. Don’t be afraid to do more research if you discover a new thread as you’re writing. More info on the research process is available in our "Conducting Research" resources .

As you’re doing your research, create an annotated bibliography ( see our page on the this type of document ). Much of the information used in an annotated bibliography can be used also in a literature review, so you’ll be not only partially drafting your lit review as you research, but also developing your sense of the larger conversation going on among scholars, professionals, and any other stakeholders in your topic.

Usually you will need to synthesize research rather than just summarizing it. This means drawing connections between sources to create a picture of the scholarly conversation on a topic over time. Many student writers struggle to synthesize because they feel they don’t have anything to add to the scholars they are citing; here are some strategies to help you:

• It often helps to remember that the point of these kinds of syntheses is to show your readers how you understand your research, to help them read the rest of your paper.
• Writing teachers often say synthesis is like hosting a dinner party: imagine all your sources are together in a room, discussing your topic. What are they saying to each other?
• Look at the in-text citations in each paragraph. Are you citing just one source for each paragraph? This usually indicates summary only. When you have multiple sources cited in a paragraph, you are more likely to be synthesizing them (not always, but often
• Read more about synthesis here.

The most interesting literature reviews are often written as arguments (again, as mentioned at the beginning of the page, this is discipline-specific and doesn’t work for all situations). Often, the literature review is where you can establish your research as filling a particular gap or as relevant in a particular way. You have some chance to do this in your introduction in an article, but the literature review section gives a more extended opportunity to establish the conversation in the way you would like your readers to see it. You can choose the intellectual lineage you would like to be part of and whose definitions matter most to your thinking (mostly humanities-specific, but this goes for sciences as well). In addressing these points, you argue for your place in the conversation, which tends to make the lit review more compelling than a simple reporting of other sources.

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What is a Literature Review? How to Write It (with Examples)

A literature review is a critical analysis and synthesis of existing research on a particular topic. It provides an overview of the current state of knowledge, identifies gaps, and highlights key findings in the literature. 1 The purpose of a literature review is to situate your own research within the context of existing scholarship, demonstrating your understanding of the topic and showing how your work contributes to the ongoing conversation in the field. Learning how to write a literature review is a critical tool for successful research. Your ability to summarize and synthesize prior research pertaining to a certain topic demonstrates your grasp on the topic of study, and assists in the learning process. 

Table of Contents

• What is the purpose of literature review? 
• a. Habitat Loss and Species Extinction: 
• b. Range Shifts and Phenological Changes: 
• c. Ocean Acidification and Coral Reefs: 
• d. Adaptive Strategies and Conservation Efforts: 

How to write a good literature review 

• Choose a Topic and Define the Research Question: 
• Decide on the Scope of Your Review: 
• Select Databases for Searches: 
• Conduct Searches and Keep Track: 
• Review the Literature: 
• Organize and Write Your Literature Review: 
• How to write a literature review faster with Paperpal? 
• Frequently asked questions 

What is a literature review?

A well-conducted literature review demonstrates the researcher’s familiarity with the existing literature, establishes the context for their own research, and contributes to scholarly conversations on the topic. One of the purposes of a literature review is also to help researchers avoid duplicating previous work and ensure that their research is informed by and builds upon the existing body of knowledge.

What is the purpose of literature review?

A literature review serves several important purposes within academic and research contexts. Here are some key objectives and functions of a literature review: 2  

1. Contextualizing the Research Problem: The literature review provides a background and context for the research problem under investigation. It helps to situate the study within the existing body of knowledge. 

2. Identifying Gaps in Knowledge: By identifying gaps, contradictions, or areas requiring further research, the researcher can shape the research question and justify the significance of the study. This is crucial for ensuring that the new research contributes something novel to the field. 

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3. Understanding Theoretical and Conceptual Frameworks: Literature reviews help researchers gain an understanding of the theoretical and conceptual frameworks used in previous studies. This aids in the development of a theoretical framework for the current research. 

4. Providing Methodological Insights: Another purpose of literature reviews is that it allows researchers to learn about the methodologies employed in previous studies. This can help in choosing appropriate research methods for the current study and avoiding pitfalls that others may have encountered. 

5. Establishing Credibility: A well-conducted literature review demonstrates the researcher’s familiarity with existing scholarship, establishing their credibility and expertise in the field. It also helps in building a solid foundation for the new research. 

6. Informing Hypotheses or Research Questions: The literature review guides the formulation of hypotheses or research questions by highlighting relevant findings and areas of uncertainty in existing literature. 

Literature review example

Let’s delve deeper with a literature review example: Let’s say your literature review is about the impact of climate change on biodiversity. You might format your literature review into sections such as the effects of climate change on habitat loss and species extinction, phenological changes, and marine biodiversity. Each section would then summarize and analyze relevant studies in those areas, highlighting key findings and identifying gaps in the research. The review would conclude by emphasizing the need for further research on specific aspects of the relationship between climate change and biodiversity. The following literature review template provides a glimpse into the recommended literature review structure and content, demonstrating how research findings are organized around specific themes within a broader topic. 

Literature Review on Climate Change Impacts on Biodiversity:

Climate change is a global phenomenon with far-reaching consequences, including significant impacts on biodiversity. This literature review synthesizes key findings from various studies: 

a. Habitat Loss and Species Extinction:

Climate change-induced alterations in temperature and precipitation patterns contribute to habitat loss, affecting numerous species (Thomas et al., 2004). The review discusses how these changes increase the risk of extinction, particularly for species with specific habitat requirements. 

b. Range Shifts and Phenological Changes:

Observations of range shifts and changes in the timing of biological events (phenology) are documented in response to changing climatic conditions (Parmesan & Yohe, 2003). These shifts affect ecosystems and may lead to mismatches between species and their resources. 

c. Ocean Acidification and Coral Reefs:

The review explores the impact of climate change on marine biodiversity, emphasizing ocean acidification’s threat to coral reefs (Hoegh-Guldberg et al., 2007). Changes in pH levels negatively affect coral calcification, disrupting the delicate balance of marine ecosystems. 

d. Adaptive Strategies and Conservation Efforts:

Recognizing the urgency of the situation, the literature review discusses various adaptive strategies adopted by species and conservation efforts aimed at mitigating the impacts of climate change on biodiversity (Hannah et al., 2007). It emphasizes the importance of interdisciplinary approaches for effective conservation planning. 

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Writing a literature review involves summarizing and synthesizing existing research on a particular topic. A good literature review format should include the following elements. 

Introduction: The introduction sets the stage for your literature review, providing context and introducing the main focus of your review. 

• Opening Statement: Begin with a general statement about the broader topic and its significance in the field. 
• Scope and Purpose: Clearly define the scope of your literature review. Explain the specific research question or objective you aim to address. 
• Organizational Framework: Briefly outline the structure of your literature review, indicating how you will categorize and discuss the existing research. 
• Significance of the Study: Highlight why your literature review is important and how it contributes to the understanding of the chosen topic. 
• Thesis Statement: Conclude the introduction with a concise thesis statement that outlines the main argument or perspective you will develop in the body of the literature review. 

Body: The body of the literature review is where you provide a comprehensive analysis of existing literature, grouping studies based on themes, methodologies, or other relevant criteria. 

• Organize by Theme or Concept: Group studies that share common themes, concepts, or methodologies. Discuss each theme or concept in detail, summarizing key findings and identifying gaps or areas of disagreement. 
• Critical Analysis: Evaluate the strengths and weaknesses of each study. Discuss the methodologies used, the quality of evidence, and the overall contribution of each work to the understanding of the topic. 
• Synthesis of Findings: Synthesize the information from different studies to highlight trends, patterns, or areas of consensus in the literature. 
• Identification of Gaps: Discuss any gaps or limitations in the existing research and explain how your review contributes to filling these gaps. 
• Transition between Sections: Provide smooth transitions between different themes or concepts to maintain the flow of your literature review. 

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Conclusion: The conclusion of your literature review should summarize the main findings, highlight the contributions of the review, and suggest avenues for future research. 

• Summary of Key Findings: Recap the main findings from the literature and restate how they contribute to your research question or objective. 
• Contributions to the Field: Discuss the overall contribution of your literature review to the existing knowledge in the field. 
• Implications and Applications: Explore the practical implications of the findings and suggest how they might impact future research or practice. 
• Recommendations for Future Research: Identify areas that require further investigation and propose potential directions for future research in the field. 
• Final Thoughts: Conclude with a final reflection on the importance of your literature review and its relevance to the broader academic community. 

Conducting a literature review

Conducting a literature review is an essential step in research that involves reviewing and analyzing existing literature on a specific topic. It’s important to know how to do a literature review effectively, so here are the steps to follow: 1  

Choose a Topic and Define the Research Question:

• Select a topic that is relevant to your field of study. 
• Clearly define your research question or objective. Determine what specific aspect of the topic do you want to explore? 

Decide on the Scope of Your Review:

• Determine the timeframe for your literature review. Are you focusing on recent developments, or do you want a historical overview? 
• Consider the geographical scope. Is your review global, or are you focusing on a specific region? 
• Define the inclusion and exclusion criteria. What types of sources will you include? Are there specific types of studies or publications you will exclude? 

Select Databases for Searches:

• Identify relevant databases for your field. Examples include PubMed, IEEE Xplore, Scopus, Web of Science, and Google Scholar. 
• Consider searching in library catalogs, institutional repositories, and specialized databases related to your topic. 

Conduct Searches and Keep Track:

• Develop a systematic search strategy using keywords, Boolean operators (AND, OR, NOT), and other search techniques. 
• Record and document your search strategy for transparency and replicability. 
• Keep track of the articles, including publication details, abstracts, and links. Use citation management tools like EndNote, Zotero, or Mendeley to organize your references. 

Review the Literature:

• Evaluate the relevance and quality of each source. Consider the methodology, sample size, and results of studies. 
• Organize the literature by themes or key concepts. Identify patterns, trends, and gaps in the existing research. 
• Summarize key findings and arguments from each source. Compare and contrast different perspectives. 
• Identify areas where there is a consensus in the literature and where there are conflicting opinions. 
• Provide critical analysis and synthesis of the literature. What are the strengths and weaknesses of existing research? 

Organize and Write Your Literature Review:

• Literature review outline should be based on themes, chronological order, or methodological approaches. 
• Write a clear and coherent narrative that synthesizes the information gathered. 
• Use proper citations for each source and ensure consistency in your citation style (APA, MLA, Chicago, etc.). 
• Conclude your literature review by summarizing key findings, identifying gaps, and suggesting areas for future research. 

Whether you’re exploring a new research field or finding new angles to develop an existing topic, sifting through hundreds of papers can take more time than you have to spare. But what if you could find science-backed insights with verified citations in seconds? That’s the power of Paperpal’s new Research feature!  

How to write a literature review faster with Paperpal?

Paperpal, an AI writing assistant, integrates powerful academic search capabilities within its writing platform. With the Research feature, you get 100% factual insights, with citations backed by 250M+ verified research articles, directly within your writing interface with the option to save relevant references in your Citation Library. By eliminating the need to switch tabs to find answers to all your research questions, Paperpal saves time and helps you stay focused on your writing.   

Here’s how to use the Research feature:  

• Ask a question: Get started with a new document on paperpal.com. Click on the “Research” feature and type your question in plain English. Paperpal will scour over 250 million research articles, including conference papers and preprints, to provide you with accurate insights and citations. 
• Review and Save: Paperpal summarizes the information, while citing sources and listing relevant reads. You can quickly scan the results to identify relevant references and save these directly to your built-in citations library for later access. 
• Cite with Confidence: Paperpal makes it easy to incorporate relevant citations and references into your writing, ensuring your arguments are well-supported by credible sources. This translates to a polished, well-researched literature review. 

The literature review sample and detailed advice on writing and conducting a review will help you produce a well-structured report. But remember that a good literature review is an ongoing process, and it may be necessary to revisit and update it as your research progresses. By combining effortless research with an easy citation process, Paperpal Research streamlines the literature review process and empowers you to write faster and with more confidence. Try Paperpal Research now and see for yourself.  

Frequently asked questions

A literature review is a critical and comprehensive analysis of existing literature (published and unpublished works) on a specific topic or research question and provides a synthesis of the current state of knowledge in a particular field. A well-conducted literature review is crucial for researchers to build upon existing knowledge, avoid duplication of efforts, and contribute to the advancement of their field. It also helps researchers situate their work within a broader context and facilitates the development of a sound theoretical and conceptual framework for their studies.

Literature review is a crucial component of research writing, providing a solid background for a research paper’s investigation. The aim is to keep professionals up to date by providing an understanding of ongoing developments within a specific field, including research methods, and experimental techniques used in that field, and present that knowledge in the form of a written report. Also, the depth and breadth of the literature review emphasizes the credibility of the scholar in his or her field.  

Before writing a literature review, it’s essential to undertake several preparatory steps to ensure that your review is well-researched, organized, and focused. This includes choosing a topic of general interest to you and doing exploratory research on that topic, writing an annotated bibliography, and noting major points, especially those that relate to the position you have taken on the topic. 

Literature reviews and academic research papers are essential components of scholarly work but serve different purposes within the academic realm. 3 A literature review aims to provide a foundation for understanding the current state of research on a particular topic, identify gaps or controversies, and lay the groundwork for future research. Therefore, it draws heavily from existing academic sources, including books, journal articles, and other scholarly publications. In contrast, an academic research paper aims to present new knowledge, contribute to the academic discourse, and advance the understanding of a specific research question. Therefore, it involves a mix of existing literature (in the introduction and literature review sections) and original data or findings obtained through research methods. 

Literature reviews are essential components of academic and research papers, and various strategies can be employed to conduct them effectively. If you want to know how to write a literature review for a research paper, here are four common approaches that are often used by researchers.  Chronological Review: This strategy involves organizing the literature based on the chronological order of publication. It helps to trace the development of a topic over time, showing how ideas, theories, and research have evolved.  Thematic Review: Thematic reviews focus on identifying and analyzing themes or topics that cut across different studies. Instead of organizing the literature chronologically, it is grouped by key themes or concepts, allowing for a comprehensive exploration of various aspects of the topic.  Methodological Review: This strategy involves organizing the literature based on the research methods employed in different studies. It helps to highlight the strengths and weaknesses of various methodologies and allows the reader to evaluate the reliability and validity of the research findings.  Theoretical Review: A theoretical review examines the literature based on the theoretical frameworks used in different studies. This approach helps to identify the key theories that have been applied to the topic and assess their contributions to the understanding of the subject.  It’s important to note that these strategies are not mutually exclusive, and a literature review may combine elements of more than one approach. The choice of strategy depends on the research question, the nature of the literature available, and the goals of the review. Additionally, other strategies, such as integrative reviews or systematic reviews, may be employed depending on the specific requirements of the research.

The literature review format can vary depending on the specific publication guidelines. However, there are some common elements and structures that are often followed. Here is a general guideline for the format of a literature review:  Introduction:   Provide an overview of the topic.  Define the scope and purpose of the literature review.  State the research question or objective.  Body:   Organize the literature by themes, concepts, or chronology.  Critically analyze and evaluate each source.  Discuss the strengths and weaknesses of the studies.  Highlight any methodological limitations or biases.  Identify patterns, connections, or contradictions in the existing research.  Conclusion:   Summarize the key points discussed in the literature review.  Highlight the research gap.  Address the research question or objective stated in the introduction.  Highlight the contributions of the review and suggest directions for future research.

Both annotated bibliographies and literature reviews involve the examination of scholarly sources. While annotated bibliographies focus on individual sources with brief annotations, literature reviews provide a more in-depth, integrated, and comprehensive analysis of existing literature on a specific topic. The key differences are as follows: 

References 

• Denney, A. S., & Tewksbury, R. (2013). How to write a literature review.  Journal of criminal justice education ,  24 (2), 218-234. 
• Pan, M. L. (2016).  Preparing literature reviews: Qualitative and quantitative approaches . Taylor & Francis. 
• Cantero, C. (2019). How to write a literature review.  San José State University Writing Center . 

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• UConn Library
• Literature Review: The What, Why and How-to Guide
• Introduction

Literature Review: The What, Why and How-to Guide — Introduction

• Getting Started
• How to Pick a Topic
• Strategies to Find Sources
• Evaluating Sources & Lit. Reviews
• Tips for Writing Literature Reviews
• Writing Literature Review: Useful Sites
• Citation Resources
• Other Academic Writings

What are Literature Reviews?

So, what is a literature review? "A literature review is an account of what has been published on a topic by accredited scholars and researchers. In writing the literature review, your purpose is to convey to your reader what knowledge and ideas have been established on a topic, and what their strengths and weaknesses are. As a piece of writing, the literature review must be defined by a guiding concept (e.g., your research objective, the problem or issue you are discussing, or your argumentative thesis). It is not just a descriptive list of the material available, or a set of summaries." Taylor, D.  The literature review: A few tips on conducting it . University of Toronto Health Sciences Writing Centre.

Goals of Literature Reviews

What are the goals of creating a Literature Review?  A literature could be written to accomplish different aims:

• To develop a theory or evaluate an existing theory
• To summarize the historical or existing state of a research topic
• Identify a problem in a field of research 

Baumeister, R. F., & Leary, M. R. (1997). Writing narrative literature reviews .  Review of General Psychology , 1 (3), 311-320.

What kinds of sources require a Literature Review?

• A research paper assigned in a course
• A thesis or dissertation
• A grant proposal
• An article intended for publication in a journal

All these instances require you to collect what has been written about your research topic so that you can demonstrate how your own research sheds new light on the topic.

Types of Literature Reviews

What kinds of literature reviews are written?

Narrative review: The purpose of this type of review is to describe the current state of the research on a specific topic/research and to offer a critical analysis of the literature reviewed. Studies are grouped by research/theoretical categories, and themes and trends, strengths and weakness, and gaps are identified. The review ends with a conclusion section which summarizes the findings regarding the state of the research of the specific study, the gaps identify and if applicable, explains how the author's research will address gaps identify in the review and expand the knowledge on the topic reviewed.

• Example : Predictors and Outcomes of U.S. Quality Maternity Leave: A Review and Conceptual Framework:  10.1177/08948453211037398  

Systematic review : "The authors of a systematic review use a specific procedure to search the research literature, select the studies to include in their review, and critically evaluate the studies they find." (p. 139). Nelson, L. K. (2013). Research in Communication Sciences and Disorders . Plural Publishing.

• Example : The effect of leave policies on increasing fertility: a systematic review:  10.1057/s41599-022-01270-w

Meta-analysis : "Meta-analysis is a method of reviewing research findings in a quantitative fashion by transforming the data from individual studies into what is called an effect size and then pooling and analyzing this information. The basic goal in meta-analysis is to explain why different outcomes have occurred in different studies." (p. 197). Roberts, M. C., & Ilardi, S. S. (2003). Handbook of Research Methods in Clinical Psychology . Blackwell Publishing.

• Example : Employment Instability and Fertility in Europe: A Meta-Analysis:  10.1215/00703370-9164737

Meta-synthesis : "Qualitative meta-synthesis is a type of qualitative study that uses as data the findings from other qualitative studies linked by the same or related topic." (p.312). Zimmer, L. (2006). Qualitative meta-synthesis: A question of dialoguing with texts .  Journal of Advanced Nursing , 53 (3), 311-318.

• Example : Women’s perspectives on career successes and barriers: A qualitative meta-synthesis:  10.1177/05390184221113735

Literature Reviews in the Health Sciences

• UConn Health subject guide on systematic reviews Explanation of the different review types used in health sciences literature as well as tools to help you find the right review type
• << Previous: Getting Started
• Next: How to Pick a Topic >>
• Last Updated: Sep 21, 2022 2:16 PM
• URL: https://guides.lib.uconn.edu/literaturereview

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• What is a Literature Review? | Guide, Template, & Examples

What is a Literature Review? | Guide, Template, & Examples

Published on 22 February 2022 by Shona McCombes . Revised on 7 June 2022.

What is a literature review? A literature review is a survey of scholarly sources on a specific topic. It provides an overview of current knowledge, allowing you to identify relevant theories, methods, and gaps in the existing research.

There are five key steps to writing a literature review:

• Search for relevant literature
• Evaluate sources
• Identify themes, debates and gaps
• Outline the structure
• Write your literature review

A good literature review doesn’t just summarise sources – it analyses, synthesises, and critically evaluates to give a clear picture of the state of knowledge on the subject.

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Table of contents

Why write a literature review, examples of literature reviews, step 1: search for relevant literature, step 2: evaluate and select sources, step 3: identify themes, debates and gaps, step 4: outline your literature review’s structure, step 5: write your literature review, frequently asked questions about literature reviews, introduction.

• Quick Run-through
• Step 1 & 2

When you write a dissertation or thesis, you will have to conduct a literature review to situate your research within existing knowledge. The literature review gives you a chance to:

• Demonstrate your familiarity with the topic and scholarly context
• Develop a theoretical framework and methodology for your research
• Position yourself in relation to other researchers and theorists
• Show how your dissertation addresses a gap or contributes to a debate

You might also have to write a literature review as a stand-alone assignment. In this case, the purpose is to evaluate the current state of research and demonstrate your knowledge of scholarly debates around a topic.

The content will look slightly different in each case, but the process of conducting a literature review follows the same steps. We’ve written a step-by-step guide that you can follow below.

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Writing literature reviews can be quite challenging! A good starting point could be to look at some examples, depending on what kind of literature review you’d like to write.

• Example literature review #1: “Why Do People Migrate? A Review of the Theoretical Literature” ( Theoretical literature review about the development of economic migration theory from the 1950s to today.)
• Example literature review #2: “Literature review as a research methodology: An overview and guidelines” ( Methodological literature review about interdisciplinary knowledge acquisition and production.)
• Example literature review #3: “The Use of Technology in English Language Learning: A Literature Review” ( Thematic literature review about the effects of technology on language acquisition.)
• Example literature review #4: “Learners’ Listening Comprehension Difficulties in English Language Learning: A Literature Review” ( Chronological literature review about how the concept of listening skills has changed over time.)

You can also check out our templates with literature review examples and sample outlines at the links below.

Download Word doc Download Google doc

Before you begin searching for literature, you need a clearly defined topic .

If you are writing the literature review section of a dissertation or research paper, you will search for literature related to your research objectives and questions .

If you are writing a literature review as a stand-alone assignment, you will have to choose a focus and develop a central question to direct your search. Unlike a dissertation research question, this question has to be answerable without collecting original data. You should be able to answer it based only on a review of existing publications.

Make a list of keywords

Start by creating a list of keywords related to your research topic. Include each of the key concepts or variables you’re interested in, and list any synonyms and related terms. You can add to this list if you discover new keywords in the process of your literature search.

• Social media, Facebook, Instagram, Twitter, Snapchat, TikTok
• Body image, self-perception, self-esteem, mental health
• Generation Z, teenagers, adolescents, youth

Search for relevant sources

Use your keywords to begin searching for sources. Some databases to search for journals and articles include:

• Your university’s library catalogue
• Google Scholar
• Project Muse (humanities and social sciences)
• Medline (life sciences and biomedicine)
• EconLit (economics)
• Inspec (physics, engineering and computer science)

You can use boolean operators to help narrow down your search:

Read the abstract to find out whether an article is relevant to your question. When you find a useful book or article, you can check the bibliography to find other relevant sources.

To identify the most important publications on your topic, take note of recurring citations. If the same authors, books or articles keep appearing in your reading, make sure to seek them out.

You probably won’t be able to read absolutely everything that has been written on the topic – you’ll have to evaluate which sources are most relevant to your questions.

For each publication, ask yourself:

• What question or problem is the author addressing?
• What are the key concepts and how are they defined?
• What are the key theories, models and methods? Does the research use established frameworks or take an innovative approach?
• What are the results and conclusions of the study?
• How does the publication relate to other literature in the field? Does it confirm, add to, or challenge established knowledge?
• How does the publication contribute to your understanding of the topic? What are its key insights and arguments?
• What are the strengths and weaknesses of the research?

Make sure the sources you use are credible, and make sure you read any landmark studies and major theories in your field of research.

You can find out how many times an article has been cited on Google Scholar – a high citation count means the article has been influential in the field, and should certainly be included in your literature review.

The scope of your review will depend on your topic and discipline: in the sciences you usually only review recent literature, but in the humanities you might take a long historical perspective (for example, to trace how a concept has changed in meaning over time).

Remember that you can use our template to summarise and evaluate sources you’re thinking about using!

Take notes and cite your sources

As you read, you should also begin the writing process. Take notes that you can later incorporate into the text of your literature review.

It’s important to keep track of your sources with references to avoid plagiarism . It can be helpful to make an annotated bibliography, where you compile full reference information and write a paragraph of summary and analysis for each source. This helps you remember what you read and saves time later in the process.

You can use our free APA Reference Generator for quick, correct, consistent citations.

To begin organising your literature review’s argument and structure, you need to understand the connections and relationships between the sources you’ve read. Based on your reading and notes, you can look for:

• Trends and patterns (in theory, method or results): do certain approaches become more or less popular over time?
• Themes: what questions or concepts recur across the literature?
• Debates, conflicts and contradictions: where do sources disagree?
• Pivotal publications: are there any influential theories or studies that changed the direction of the field?
• Gaps: what is missing from the literature? Are there weaknesses that need to be addressed?

This step will help you work out the structure of your literature review and (if applicable) show how your own research will contribute to existing knowledge.

• Most research has focused on young women.
• There is an increasing interest in the visual aspects of social media.
• But there is still a lack of robust research on highly-visual platforms like Instagram and Snapchat – this is a gap that you could address in your own research.

There are various approaches to organising the body of a literature review. You should have a rough idea of your strategy before you start writing.

Depending on the length of your literature review, you can combine several of these strategies (for example, your overall structure might be thematic, but each theme is discussed chronologically).

Chronological

The simplest approach is to trace the development of the topic over time. However, if you choose this strategy, be careful to avoid simply listing and summarising sources in order.

Try to analyse patterns, turning points and key debates that have shaped the direction of the field. Give your interpretation of how and why certain developments occurred.

If you have found some recurring central themes, you can organise your literature review into subsections that address different aspects of the topic.

For example, if you are reviewing literature about inequalities in migrant health outcomes, key themes might include healthcare policy, language barriers, cultural attitudes, legal status, and economic access.

Methodological

If you draw your sources from different disciplines or fields that use a variety of research methods , you might want to compare the results and conclusions that emerge from different approaches. For example:

• Look at what results have emerged in qualitative versus quantitative research
• Discuss how the topic has been approached by empirical versus theoretical scholarship
• Divide the literature into sociological, historical, and cultural sources

Theoretical

A literature review is often the foundation for a theoretical framework . You can use it to discuss various theories, models, and definitions of key concepts.

You might argue for the relevance of a specific theoretical approach, or combine various theoretical concepts to create a framework for your research.

Like any other academic text, your literature review should have an introduction , a main body, and a conclusion . What you include in each depends on the objective of your literature review.

The introduction should clearly establish the focus and purpose of the literature review.

If you are writing the literature review as part of your dissertation or thesis, reiterate your central problem or research question and give a brief summary of the scholarly context. You can emphasise the timeliness of the topic (“many recent studies have focused on the problem of x”) or highlight a gap in the literature (“while there has been much research on x, few researchers have taken y into consideration”).

Depending on the length of your literature review, you might want to divide the body into subsections. You can use a subheading for each theme, time period, or methodological approach.

As you write, make sure to follow these tips:

• Summarise and synthesise: give an overview of the main points of each source and combine them into a coherent whole.
• Analyse and interpret: don’t just paraphrase other researchers – add your own interpretations, discussing the significance of findings in relation to the literature as a whole.
• Critically evaluate: mention the strengths and weaknesses of your sources.
• Write in well-structured paragraphs: use transitions and topic sentences to draw connections, comparisons and contrasts.

In the conclusion, you should summarise the key findings you have taken from the literature and emphasise their significance.

If the literature review is part of your dissertation or thesis, reiterate how your research addresses gaps and contributes new knowledge, or discuss how you have drawn on existing theories and methods to build a framework for your research. This can lead directly into your methodology section.

A literature review is a survey of scholarly sources (such as books, journal articles, and theses) related to a specific topic or research question .

It is often written as part of a dissertation , thesis, research paper , or proposal .

There are several reasons to conduct a literature review at the beginning of a research project:

• To familiarise yourself with the current state of knowledge on your topic
• To ensure that you’re not just repeating what others have already done
• To identify gaps in knowledge and unresolved problems that your research can address
• To develop your theoretical framework and methodology
• To provide an overview of the key findings and debates on the topic

Writing the literature review shows your reader how your work relates to existing research and what new insights it will contribute.

The literature review usually comes near the beginning of your  dissertation . After the introduction , it grounds your research in a scholarly field and leads directly to your theoretical framework or methodology .

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Ten Simple Rules for Writing a Literature Review

Marco pautasso.

1 Centre for Functional and Evolutionary Ecology (CEFE), CNRS, Montpellier, France

2 Centre for Biodiversity Synthesis and Analysis (CESAB), FRB, Aix-en-Provence, France

Literature reviews are in great demand in most scientific fields. Their need stems from the ever-increasing output of scientific publications [1] . For example, compared to 1991, in 2008 three, eight, and forty times more papers were indexed in Web of Science on malaria, obesity, and biodiversity, respectively [2] . Given such mountains of papers, scientists cannot be expected to examine in detail every single new paper relevant to their interests [3] . Thus, it is both advantageous and necessary to rely on regular summaries of the recent literature. Although recognition for scientists mainly comes from primary research, timely literature reviews can lead to new synthetic insights and are often widely read [4] . For such summaries to be useful, however, they need to be compiled in a professional way [5] .

When starting from scratch, reviewing the literature can require a titanic amount of work. That is why researchers who have spent their career working on a certain research issue are in a perfect position to review that literature. Some graduate schools are now offering courses in reviewing the literature, given that most research students start their project by producing an overview of what has already been done on their research issue [6] . However, it is likely that most scientists have not thought in detail about how to approach and carry out a literature review.

Reviewing the literature requires the ability to juggle multiple tasks, from finding and evaluating relevant material to synthesising information from various sources, from critical thinking to paraphrasing, evaluating, and citation skills [7] . In this contribution, I share ten simple rules I learned working on about 25 literature reviews as a PhD and postdoctoral student. Ideas and insights also come from discussions with coauthors and colleagues, as well as feedback from reviewers and editors.

Rule 1: Define a Topic and Audience

How to choose which topic to review? There are so many issues in contemporary science that you could spend a lifetime of attending conferences and reading the literature just pondering what to review. On the one hand, if you take several years to choose, several other people may have had the same idea in the meantime. On the other hand, only a well-considered topic is likely to lead to a brilliant literature review [8] . The topic must at least be:

• interesting to you (ideally, you should have come across a series of recent papers related to your line of work that call for a critical summary),
• an important aspect of the field (so that many readers will be interested in the review and there will be enough material to write it), and
• a well-defined issue (otherwise you could potentially include thousands of publications, which would make the review unhelpful).

Ideas for potential reviews may come from papers providing lists of key research questions to be answered [9] , but also from serendipitous moments during desultory reading and discussions. In addition to choosing your topic, you should also select a target audience. In many cases, the topic (e.g., web services in computational biology) will automatically define an audience (e.g., computational biologists), but that same topic may also be of interest to neighbouring fields (e.g., computer science, biology, etc.).

Rule 2: Search and Re-search the Literature

After having chosen your topic and audience, start by checking the literature and downloading relevant papers. Five pieces of advice here:

• keep track of the search items you use (so that your search can be replicated [10] ),
• keep a list of papers whose pdfs you cannot access immediately (so as to retrieve them later with alternative strategies),
• use a paper management system (e.g., Mendeley, Papers, Qiqqa, Sente),
• define early in the process some criteria for exclusion of irrelevant papers (these criteria can then be described in the review to help define its scope), and
• do not just look for research papers in the area you wish to review, but also seek previous reviews.

The chances are high that someone will already have published a literature review ( Figure 1 ), if not exactly on the issue you are planning to tackle, at least on a related topic. If there are already a few or several reviews of the literature on your issue, my advice is not to give up, but to carry on with your own literature review,

The bottom-right situation (many literature reviews but few research papers) is not just a theoretical situation; it applies, for example, to the study of the impacts of climate change on plant diseases, where there appear to be more literature reviews than research studies [33] .

• discussing in your review the approaches, limitations, and conclusions of past reviews,
• trying to find a new angle that has not been covered adequately in the previous reviews, and
• incorporating new material that has inevitably accumulated since their appearance.

When searching the literature for pertinent papers and reviews, the usual rules apply:

• be thorough,
• use different keywords and database sources (e.g., DBLP, Google Scholar, ISI Proceedings, JSTOR Search, Medline, Scopus, Web of Science), and
• look at who has cited past relevant papers and book chapters.

Rule 3: Take Notes While Reading

If you read the papers first, and only afterwards start writing the review, you will need a very good memory to remember who wrote what, and what your impressions and associations were while reading each single paper. My advice is, while reading, to start writing down interesting pieces of information, insights about how to organize the review, and thoughts on what to write. This way, by the time you have read the literature you selected, you will already have a rough draft of the review.

Of course, this draft will still need much rewriting, restructuring, and rethinking to obtain a text with a coherent argument [11] , but you will have avoided the danger posed by staring at a blank document. Be careful when taking notes to use quotation marks if you are provisionally copying verbatim from the literature. It is advisable then to reformulate such quotes with your own words in the final draft. It is important to be careful in noting the references already at this stage, so as to avoid misattributions. Using referencing software from the very beginning of your endeavour will save you time.

Rule 4: Choose the Type of Review You Wish to Write

After having taken notes while reading the literature, you will have a rough idea of the amount of material available for the review. This is probably a good time to decide whether to go for a mini- or a full review. Some journals are now favouring the publication of rather short reviews focusing on the last few years, with a limit on the number of words and citations. A mini-review is not necessarily a minor review: it may well attract more attention from busy readers, although it will inevitably simplify some issues and leave out some relevant material due to space limitations. A full review will have the advantage of more freedom to cover in detail the complexities of a particular scientific development, but may then be left in the pile of the very important papers “to be read” by readers with little time to spare for major monographs.

There is probably a continuum between mini- and full reviews. The same point applies to the dichotomy of descriptive vs. integrative reviews. While descriptive reviews focus on the methodology, findings, and interpretation of each reviewed study, integrative reviews attempt to find common ideas and concepts from the reviewed material [12] . A similar distinction exists between narrative and systematic reviews: while narrative reviews are qualitative, systematic reviews attempt to test a hypothesis based on the published evidence, which is gathered using a predefined protocol to reduce bias [13] , [14] . When systematic reviews analyse quantitative results in a quantitative way, they become meta-analyses. The choice between different review types will have to be made on a case-by-case basis, depending not just on the nature of the material found and the preferences of the target journal(s), but also on the time available to write the review and the number of coauthors [15] .

Rule 5: Keep the Review Focused, but Make It of Broad Interest

Whether your plan is to write a mini- or a full review, it is good advice to keep it focused 16 , 17 . Including material just for the sake of it can easily lead to reviews that are trying to do too many things at once. The need to keep a review focused can be problematic for interdisciplinary reviews, where the aim is to bridge the gap between fields [18] . If you are writing a review on, for example, how epidemiological approaches are used in modelling the spread of ideas, you may be inclined to include material from both parent fields, epidemiology and the study of cultural diffusion. This may be necessary to some extent, but in this case a focused review would only deal in detail with those studies at the interface between epidemiology and the spread of ideas.

While focus is an important feature of a successful review, this requirement has to be balanced with the need to make the review relevant to a broad audience. This square may be circled by discussing the wider implications of the reviewed topic for other disciplines.

Rule 6: Be Critical and Consistent

Reviewing the literature is not stamp collecting. A good review does not just summarize the literature, but discusses it critically, identifies methodological problems, and points out research gaps [19] . After having read a review of the literature, a reader should have a rough idea of:

• the major achievements in the reviewed field,
• the main areas of debate, and
• the outstanding research questions.

It is challenging to achieve a successful review on all these fronts. A solution can be to involve a set of complementary coauthors: some people are excellent at mapping what has been achieved, some others are very good at identifying dark clouds on the horizon, and some have instead a knack at predicting where solutions are going to come from. If your journal club has exactly this sort of team, then you should definitely write a review of the literature! In addition to critical thinking, a literature review needs consistency, for example in the choice of passive vs. active voice and present vs. past tense.

Rule 7: Find a Logical Structure

Like a well-baked cake, a good review has a number of telling features: it is worth the reader's time, timely, systematic, well written, focused, and critical. It also needs a good structure. With reviews, the usual subdivision of research papers into introduction, methods, results, and discussion does not work or is rarely used. However, a general introduction of the context and, toward the end, a recapitulation of the main points covered and take-home messages make sense also in the case of reviews. For systematic reviews, there is a trend towards including information about how the literature was searched (database, keywords, time limits) [20] .

How can you organize the flow of the main body of the review so that the reader will be drawn into and guided through it? It is generally helpful to draw a conceptual scheme of the review, e.g., with mind-mapping techniques. Such diagrams can help recognize a logical way to order and link the various sections of a review [21] . This is the case not just at the writing stage, but also for readers if the diagram is included in the review as a figure. A careful selection of diagrams and figures relevant to the reviewed topic can be very helpful to structure the text too [22] .

Rule 8: Make Use of Feedback

Reviews of the literature are normally peer-reviewed in the same way as research papers, and rightly so [23] . As a rule, incorporating feedback from reviewers greatly helps improve a review draft. Having read the review with a fresh mind, reviewers may spot inaccuracies, inconsistencies, and ambiguities that had not been noticed by the writers due to rereading the typescript too many times. It is however advisable to reread the draft one more time before submission, as a last-minute correction of typos, leaps, and muddled sentences may enable the reviewers to focus on providing advice on the content rather than the form.

Feedback is vital to writing a good review, and should be sought from a variety of colleagues, so as to obtain a diversity of views on the draft. This may lead in some cases to conflicting views on the merits of the paper, and on how to improve it, but such a situation is better than the absence of feedback. A diversity of feedback perspectives on a literature review can help identify where the consensus view stands in the landscape of the current scientific understanding of an issue [24] .

Rule 9: Include Your Own Relevant Research, but Be Objective

In many cases, reviewers of the literature will have published studies relevant to the review they are writing. This could create a conflict of interest: how can reviewers report objectively on their own work [25] ? Some scientists may be overly enthusiastic about what they have published, and thus risk giving too much importance to their own findings in the review. However, bias could also occur in the other direction: some scientists may be unduly dismissive of their own achievements, so that they will tend to downplay their contribution (if any) to a field when reviewing it.

In general, a review of the literature should neither be a public relations brochure nor an exercise in competitive self-denial. If a reviewer is up to the job of producing a well-organized and methodical review, which flows well and provides a service to the readership, then it should be possible to be objective in reviewing one's own relevant findings. In reviews written by multiple authors, this may be achieved by assigning the review of the results of a coauthor to different coauthors.

Rule 10: Be Up-to-Date, but Do Not Forget Older Studies

Given the progressive acceleration in the publication of scientific papers, today's reviews of the literature need awareness not just of the overall direction and achievements of a field of inquiry, but also of the latest studies, so as not to become out-of-date before they have been published. Ideally, a literature review should not identify as a major research gap an issue that has just been addressed in a series of papers in press (the same applies, of course, to older, overlooked studies (“sleeping beauties” [26] )). This implies that literature reviewers would do well to keep an eye on electronic lists of papers in press, given that it can take months before these appear in scientific databases. Some reviews declare that they have scanned the literature up to a certain point in time, but given that peer review can be a rather lengthy process, a full search for newly appeared literature at the revision stage may be worthwhile. Assessing the contribution of papers that have just appeared is particularly challenging, because there is little perspective with which to gauge their significance and impact on further research and society.

Inevitably, new papers on the reviewed topic (including independently written literature reviews) will appear from all quarters after the review has been published, so that there may soon be the need for an updated review. But this is the nature of science [27] – [32] . I wish everybody good luck with writing a review of the literature.

Acknowledgments

Many thanks to M. Barbosa, K. Dehnen-Schmutz, T. Döring, D. Fontaneto, M. Garbelotto, O. Holdenrieder, M. Jeger, D. Lonsdale, A. MacLeod, P. Mills, M. Moslonka-Lefebvre, G. Stancanelli, P. Weisberg, and X. Xu for insights and discussions, and to P. Bourne, T. Matoni, and D. Smith for helpful comments on a previous draft.

Funding Statement

This work was funded by the French Foundation for Research on Biodiversity (FRB) through its Centre for Synthesis and Analysis of Biodiversity data (CESAB), as part of the NETSEED research project. The funders had no role in the preparation of the manuscript.

Literature Reviews

What this handout is about.

This handout will explain what literature reviews are and offer insights into the form and construction of literature reviews in the humanities, social sciences, and sciences.

Introduction

OK. You’ve got to write a literature review. You dust off a novel and a book of poetry, settle down in your chair, and get ready to issue a “thumbs up” or “thumbs down” as you leaf through the pages. “Literature review” done. Right?

Wrong! The “literature” of a literature review refers to any collection of materials on a topic, not necessarily the great literary texts of the world. “Literature” could be anything from a set of government pamphlets on British colonial methods in Africa to scholarly articles on the treatment of a torn ACL. And a review does not necessarily mean that your reader wants you to give your personal opinion on whether or not you liked these sources.

What is a literature review, then?

A literature review discusses published information in a particular subject area, and sometimes information in a particular subject area within a certain time period.

A literature review can be just a simple summary of the sources, but it usually has an organizational pattern and combines both summary and synthesis. A summary is a recap of the important information of the source, but a synthesis is a re-organization, or a reshuffling, of that information. It might give a new interpretation of old material or combine new with old interpretations. Or it might trace the intellectual progression of the field, including major debates. And depending on the situation, the literature review may evaluate the sources and advise the reader on the most pertinent or relevant.

But how is a literature review different from an academic research paper?

The main focus of an academic research paper is to develop a new argument, and a research paper is likely to contain a literature review as one of its parts. In a research paper, you use the literature as a foundation and as support for a new insight that you contribute. The focus of a literature review, however, is to summarize and synthesize the arguments and ideas of others without adding new contributions.

Why do we write literature reviews?

Literature reviews provide you with a handy guide to a particular topic. If you have limited time to conduct research, literature reviews can give you an overview or act as a stepping stone. For professionals, they are useful reports that keep them up to date with what is current in the field. For scholars, the depth and breadth of the literature review emphasizes the credibility of the writer in his or her field. Literature reviews also provide a solid background for a research paper’s investigation. Comprehensive knowledge of the literature of the field is essential to most research papers.

Who writes these things, anyway?

Literature reviews are written occasionally in the humanities, but mostly in the sciences and social sciences; in experiment and lab reports, they constitute a section of the paper. Sometimes a literature review is written as a paper in itself.

Let’s get to it! What should I do before writing the literature review?

If your assignment is not very specific, seek clarification from your instructor:

• Roughly how many sources should you include?
• What types of sources (books, journal articles, websites)?
• Should you summarize, synthesize, or critique your sources by discussing a common theme or issue?
• Should you evaluate your sources?
• Should you provide subheadings and other background information, such as definitions and/or a history?

Find models

Look for other literature reviews in your area of interest or in the discipline and read them to get a sense of the types of themes you might want to look for in your own research or ways to organize your final review. You can simply put the word “review” in your search engine along with your other topic terms to find articles of this type on the Internet or in an electronic database. The bibliography or reference section of sources you’ve already read are also excellent entry points into your own research.

Narrow your topic

There are hundreds or even thousands of articles and books on most areas of study. The narrower your topic, the easier it will be to limit the number of sources you need to read in order to get a good survey of the material. Your instructor will probably not expect you to read everything that’s out there on the topic, but you’ll make your job easier if you first limit your scope.

Keep in mind that UNC Libraries have research guides and to databases relevant to many fields of study. You can reach out to the subject librarian for a consultation: https://library.unc.edu/support/consultations/ .

And don’t forget to tap into your professor’s (or other professors’) knowledge in the field. Ask your professor questions such as: “If you had to read only one book from the 90’s on topic X, what would it be?” Questions such as this help you to find and determine quickly the most seminal pieces in the field.

Consider whether your sources are current

Some disciplines require that you use information that is as current as possible. In the sciences, for instance, treatments for medical problems are constantly changing according to the latest studies. Information even two years old could be obsolete. However, if you are writing a review in the humanities, history, or social sciences, a survey of the history of the literature may be what is needed, because what is important is how perspectives have changed through the years or within a certain time period. Try sorting through some other current bibliographies or literature reviews in the field to get a sense of what your discipline expects. You can also use this method to consider what is currently of interest to scholars in this field and what is not.

Strategies for writing the literature review

Find a focus.

A literature review, like a term paper, is usually organized around ideas, not the sources themselves as an annotated bibliography would be organized. This means that you will not just simply list your sources and go into detail about each one of them, one at a time. No. As you read widely but selectively in your topic area, consider instead what themes or issues connect your sources together. Do they present one or different solutions? Is there an aspect of the field that is missing? How well do they present the material and do they portray it according to an appropriate theory? Do they reveal a trend in the field? A raging debate? Pick one of these themes to focus the organization of your review.

Convey it to your reader

A literature review may not have a traditional thesis statement (one that makes an argument), but you do need to tell readers what to expect. Try writing a simple statement that lets the reader know what is your main organizing principle. Here are a couple of examples:

The current trend in treatment for congestive heart failure combines surgery and medicine. More and more cultural studies scholars are accepting popular media as a subject worthy of academic consideration.

Consider organization

You’ve got a focus, and you’ve stated it clearly and directly. Now what is the most effective way of presenting the information? What are the most important topics, subtopics, etc., that your review needs to include? And in what order should you present them? Develop an organization for your review at both a global and local level:

First, cover the basic categories

Just like most academic papers, literature reviews also must contain at least three basic elements: an introduction or background information section; the body of the review containing the discussion of sources; and, finally, a conclusion and/or recommendations section to end the paper. The following provides a brief description of the content of each:

• Introduction: Gives a quick idea of the topic of the literature review, such as the central theme or organizational pattern.
• Body: Contains your discussion of sources and is organized either chronologically, thematically, or methodologically (see below for more information on each).
• Conclusions/Recommendations: Discuss what you have drawn from reviewing literature so far. Where might the discussion proceed?

Organizing the body

Once you have the basic categories in place, then you must consider how you will present the sources themselves within the body of your paper. Create an organizational method to focus this section even further.

To help you come up with an overall organizational framework for your review, consider the following scenario:

You’ve decided to focus your literature review on materials dealing with sperm whales. This is because you’ve just finished reading Moby Dick, and you wonder if that whale’s portrayal is really real. You start with some articles about the physiology of sperm whales in biology journals written in the 1980’s. But these articles refer to some British biological studies performed on whales in the early 18th century. So you check those out. Then you look up a book written in 1968 with information on how sperm whales have been portrayed in other forms of art, such as in Alaskan poetry, in French painting, or on whale bone, as the whale hunters in the late 19th century used to do. This makes you wonder about American whaling methods during the time portrayed in Moby Dick, so you find some academic articles published in the last five years on how accurately Herman Melville portrayed the whaling scene in his novel.

Now consider some typical ways of organizing the sources into a review:

• Chronological: If your review follows the chronological method, you could write about the materials above according to when they were published. For instance, first you would talk about the British biological studies of the 18th century, then about Moby Dick, published in 1851, then the book on sperm whales in other art (1968), and finally the biology articles (1980s) and the recent articles on American whaling of the 19th century. But there is relatively no continuity among subjects here. And notice that even though the sources on sperm whales in other art and on American whaling are written recently, they are about other subjects/objects that were created much earlier. Thus, the review loses its chronological focus.
• By publication: Order your sources by publication chronology, then, only if the order demonstrates a more important trend. For instance, you could order a review of literature on biological studies of sperm whales if the progression revealed a change in dissection practices of the researchers who wrote and/or conducted the studies.
• By trend: A better way to organize the above sources chronologically is to examine the sources under another trend, such as the history of whaling. Then your review would have subsections according to eras within this period. For instance, the review might examine whaling from pre-1600-1699, 1700-1799, and 1800-1899. Under this method, you would combine the recent studies on American whaling in the 19th century with Moby Dick itself in the 1800-1899 category, even though the authors wrote a century apart.
• Thematic: Thematic reviews of literature are organized around a topic or issue, rather than the progression of time. However, progression of time may still be an important factor in a thematic review. For instance, the sperm whale review could focus on the development of the harpoon for whale hunting. While the study focuses on one topic, harpoon technology, it will still be organized chronologically. The only difference here between a “chronological” and a “thematic” approach is what is emphasized the most: the development of the harpoon or the harpoon technology.But more authentic thematic reviews tend to break away from chronological order. For instance, a thematic review of material on sperm whales might examine how they are portrayed as “evil” in cultural documents. The subsections might include how they are personified, how their proportions are exaggerated, and their behaviors misunderstood. A review organized in this manner would shift between time periods within each section according to the point made.
• Methodological: A methodological approach differs from the two above in that the focusing factor usually does not have to do with the content of the material. Instead, it focuses on the “methods” of the researcher or writer. For the sperm whale project, one methodological approach would be to look at cultural differences between the portrayal of whales in American, British, and French art work. Or the review might focus on the economic impact of whaling on a community. A methodological scope will influence either the types of documents in the review or the way in which these documents are discussed. Once you’ve decided on the organizational method for the body of the review, the sections you need to include in the paper should be easy to figure out. They should arise out of your organizational strategy. In other words, a chronological review would have subsections for each vital time period. A thematic review would have subtopics based upon factors that relate to the theme or issue.

Sometimes, though, you might need to add additional sections that are necessary for your study, but do not fit in the organizational strategy of the body. What other sections you include in the body is up to you. Put in only what is necessary. Here are a few other sections you might want to consider:

• Current Situation: Information necessary to understand the topic or focus of the literature review.
• History: The chronological progression of the field, the literature, or an idea that is necessary to understand the literature review, if the body of the literature review is not already a chronology.
• Methods and/or Standards: The criteria you used to select the sources in your literature review or the way in which you present your information. For instance, you might explain that your review includes only peer-reviewed articles and journals.

Questions for Further Research: What questions about the field has the review sparked? How will you further your research as a result of the review?

Begin composing

Once you’ve settled on a general pattern of organization, you’re ready to write each section. There are a few guidelines you should follow during the writing stage as well. Here is a sample paragraph from a literature review about sexism and language to illuminate the following discussion:

However, other studies have shown that even gender-neutral antecedents are more likely to produce masculine images than feminine ones (Gastil, 1990). Hamilton (1988) asked students to complete sentences that required them to fill in pronouns that agreed with gender-neutral antecedents such as “writer,” “pedestrian,” and “persons.” The students were asked to describe any image they had when writing the sentence. Hamilton found that people imagined 3.3 men to each woman in the masculine “generic” condition and 1.5 men per woman in the unbiased condition. Thus, while ambient sexism accounted for some of the masculine bias, sexist language amplified the effect. (Source: Erika Falk and Jordan Mills, “Why Sexist Language Affects Persuasion: The Role of Homophily, Intended Audience, and Offense,” Women and Language19:2).

Use evidence

In the example above, the writers refer to several other sources when making their point. A literature review in this sense is just like any other academic research paper. Your interpretation of the available sources must be backed up with evidence to show that what you are saying is valid.

Be selective

Select only the most important points in each source to highlight in the review. The type of information you choose to mention should relate directly to the review’s focus, whether it is thematic, methodological, or chronological.

Use quotes sparingly

Falk and Mills do not use any direct quotes. That is because the survey nature of the literature review does not allow for in-depth discussion or detailed quotes from the text. Some short quotes here and there are okay, though, if you want to emphasize a point, or if what the author said just cannot be rewritten in your own words. Notice that Falk and Mills do quote certain terms that were coined by the author, not common knowledge, or taken directly from the study. But if you find yourself wanting to put in more quotes, check with your instructor.

Summarize and synthesize

Remember to summarize and synthesize your sources within each paragraph as well as throughout the review. The authors here recapitulate important features of Hamilton’s study, but then synthesize it by rephrasing the study’s significance and relating it to their own work.

Keep your own voice

While the literature review presents others’ ideas, your voice (the writer’s) should remain front and center. Notice that Falk and Mills weave references to other sources into their own text, but they still maintain their own voice by starting and ending the paragraph with their own ideas and their own words. The sources support what Falk and Mills are saying.

Use caution when paraphrasing

When paraphrasing a source that is not your own, be sure to represent the author’s information or opinions accurately and in your own words. In the preceding example, Falk and Mills either directly refer in the text to the author of their source, such as Hamilton, or they provide ample notation in the text when the ideas they are mentioning are not their own, for example, Gastil’s. For more information, please see our handout on plagiarism .

Revise, revise, revise

Draft in hand? Now you’re ready to revise. Spending a lot of time revising is a wise idea, because your main objective is to present the material, not the argument. So check over your review again to make sure it follows the assignment and/or your outline. Then, just as you would for most other academic forms of writing, rewrite or rework the language of your review so that you’ve presented your information in the most concise manner possible. Be sure to use terminology familiar to your audience; get rid of unnecessary jargon or slang. Finally, double check that you’ve documented your sources and formatted the review appropriately for your discipline. For tips on the revising and editing process, see our handout on revising drafts .

Works consulted

We consulted these works while writing this handout. This is not a comprehensive list of resources on the handout’s topic, and we encourage you to do your own research to find additional publications. Please do not use this list as a model for the format of your own reference list, as it may not match the citation style you are using. For guidance on formatting citations, please see the UNC Libraries citation tutorial . We revise these tips periodically and welcome feedback.

Anson, Chris M., and Robert A. Schwegler. 2010. The Longman Handbook for Writers and Readers , 6th ed. New York: Longman.

Jones, Robert, Patrick Bizzaro, and Cynthia Selfe. 1997. The Harcourt Brace Guide to Writing in the Disciplines . New York: Harcourt Brace.

Lamb, Sandra E. 1998. How to Write It: A Complete Guide to Everything You’ll Ever Write . Berkeley: Ten Speed Press.

Rosen, Leonard J., and Laurence Behrens. 2003. The Allyn & Bacon Handbook , 5th ed. New York: Longman.

Troyka, Lynn Quittman, and Doug Hesse. 2016. Simon and Schuster Handbook for Writers , 11th ed. London: Pearson.

You may reproduce it for non-commercial use if you use the entire handout and attribute the source: The Writing Center, University of North Carolina at Chapel Hill

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How to Write a Literature Review

What is a literature review.

• What Is the Literature
• Writing the Review

A literature review is much more than an annotated bibliography or a list of separate reviews of articles and books. It is a critical, analytical summary and synthesis of the current knowledge of a topic. Thus it should compare and relate different theories, findings, etc, rather than just summarize them individually. In addition, it should have a particular focus or theme to organize the review. It does not have to be an exhaustive account of everything published on the topic, but it should discuss all the significant academic literature and other relevant sources important for that focus.

This is meant to be a general guide to writing a literature review: ways to structure one, what to include, how it supplements other research. For more specific help on writing a review, and especially for help on finding the literature to review, sign up for a Personal Research Session .

The specific organization of a literature review depends on the type and purpose of the review, as well as on the specific field or topic being reviewed. But in general, it is a relatively brief but thorough exploration of past and current work on a topic. Rather than a chronological listing of previous work, though, literature reviews are usually organized thematically, such as different theoretical approaches, methodologies, or specific issues or concepts involved in the topic. A thematic organization makes it much easier to examine contrasting perspectives, theoretical approaches, methodologies, findings, etc, and to analyze the strengths and weaknesses of, and point out any gaps in, previous research. And this is the heart of what a literature review is about. A literature review may offer new interpretations, theoretical approaches, or other ideas; if it is part of a research proposal or report it should demonstrate the relationship of the proposed or reported research to others' work; but whatever else it does, it must provide a critical overview of the current state of research efforts. 

Literature reviews are common and very important in the sciences and social sciences. They are less common and have a less important role in the humanities, but they do have a place, especially stand-alone reviews.

Types of Literature Reviews

There are different types of literature reviews, and different purposes for writing a review, but the most common are:

• Stand-alone literature review articles . These provide an overview and analysis of the current state of research on a topic or question. The goal is to evaluate and compare previous research on a topic to provide an analysis of what is currently known, and also to reveal controversies, weaknesses, and gaps in current work, thus pointing to directions for future research. You can find examples published in any number of academic journals, but there is a series of Annual Reviews of *Subject* which are specifically devoted to literature review articles. Writing a stand-alone review is often an effective way to get a good handle on a topic and to develop ideas for your own research program. For example, contrasting theoretical approaches or conflicting interpretations of findings can be the basis of your research project: can you find evidence supporting one interpretation against another, or can you propose an alternative interpretation that overcomes their limitations?
• Part of a research proposal . This could be a proposal for a PhD dissertation, a senior thesis, or a class project. It could also be a submission for a grant. The literature review, by pointing out the current issues and questions concerning a topic, is a crucial part of demonstrating how your proposed research will contribute to the field, and thus of convincing your thesis committee to allow you to pursue the topic of your interest or a funding agency to pay for your research efforts.
• Part of a research report . When you finish your research and write your thesis or paper to present your findings, it should include a literature review to provide the context to which your work is a contribution. Your report, in addition to detailing the methods, results, etc. of your research, should show how your work relates to others' work.

A literature review for a research report is often a revision of the review for a research proposal, which can be a revision of a stand-alone review. Each revision should be a fairly extensive revision. With the increased knowledge of and experience in the topic as you proceed, your understanding of the topic will increase. Thus, you will be in a better position to analyze and critique the literature. In addition, your focus will change as you proceed in your research. Some areas of the literature you initially reviewed will be marginal or irrelevant for your eventual research, and you will need to explore other areas more thoroughly. 

Examples of Literature Reviews

See the series of Annual Reviews of *Subject* which are specifically devoted to literature review articles to find many examples of stand-alone literature reviews in the biomedical, physical, and social sciences. 

Research report articles vary in how they are organized, but a common general structure is to have sections such as:

• Abstract - Brief summary of the contents of the article
• Introduction - A explanation of the purpose of the study, a statement of the research question(s) the study intends to address
• Literature review - A critical assessment of the work done so far on this topic, to show how the current study relates to what has already been done
• Methods - How the study was carried out (e.g. instruments or equipment, procedures, methods to gather and analyze data)
• Results - What was found in the course of the study
• Discussion - What do the results mean
• Conclusion - State the conclusions and implications of the results, and discuss how it relates to the work reviewed in the literature review; also, point to directions for further work in the area

Here are some articles that illustrate variations on this theme. There is no need to read the entire articles (unless the contents interest you); just quickly browse through to see the sections, and see how each section is introduced and what is contained in them.

The Determinants of Undergraduate Grade Point Average: The Relative Importance of Family Background, High School Resources, and Peer Group Effects , in The Journal of Human Resources , v. 34 no. 2 (Spring 1999), p. 268-293.

This article has a standard breakdown of sections:

• Introduction
• Literature Review
• Some discussion sections

First Encounters of the Bureaucratic Kind: Early Freshman Experiences with a Campus Bureaucracy , in The Journal of Higher Education , v. 67 no. 6 (Nov-Dec 1996), p. 660-691.

This one does not have a section specifically labeled as a "literature review" or "review of the literature," but the first few sections cite a long list of other sources discussing previous research in the area before the authors present their own study they are reporting.

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Introduction

Literature reviews take time. here is some general information to know before you start.  .

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What is a literature review?

A literature review is an integrated analysis -- not just a summary-- of scholarly writings and other relevant evidence related directly to your research question.  That is, it represents a synthesis of the evidence that provides background information on your topic and shows a association between the evidence and your research question.

A literature review may be a stand alone work or the introduction to a larger research paper, depending on the assignment.  Rely heavily on the guidelines your instructor has given you.

Why is it important?

A literature review is important because it:

• Explains the background of research on a topic.
• Demonstrates why a topic is significant to a subject area.
• Discovers relationships between research studies/ideas.
• Identifies major themes, concepts, and researchers on a topic.
• Identifies critical gaps and points of disagreement.
• Discusses further research questions that logically come out of the previous studies.

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1. Choose a topic. Define your research question.

Your literature review should be guided by your central research question.  The literature represents background and research developments related to a specific research question, interpreted and analyzed by you in a synthesized way.

• Make sure your research question is not too broad or too narrow.  Is it manageable?
• Begin writing down terms that are related to your question. These will be useful for searches later.
• If you have the opportunity, discuss your topic with your professor and your class mates.

2. Decide on the scope of your review

How many studies do you need to look at? How comprehensive should it be? How many years should it cover? 

• This may depend on your assignment.  How many sources does the assignment require?

3. Select the databases you will use to conduct your searches.

Make a list of the databases you will search. 

Where to find databases:

• use the tabs on this guide
• Find other databases in the Nursing Information Resources web page
• More on the Medical Library web page
• ... and more on the Yale University Library web page

4. Conduct your searches to find the evidence. Keep track of your searches.

• Use the key words in your question, as well as synonyms for those words, as terms in your search. Use the database tutorials for help.
• Save the searches in the databases. This saves time when you want to redo, or modify, the searches. It is also helpful to use as a guide is the searches are not finding any useful results.
• Review the abstracts of research studies carefully. This will save you time.
• Use the bibliographies and references of research studies you find to locate others.
• Check with your professor, or a subject expert in the field, if you are missing any key works in the field.
• Ask your librarian for help at any time.
• Use a citation manager, such as EndNote as the repository for your citations. See the EndNote tutorials for help.

Review the literature

Some questions to help you analyze the research:

• What was the research question of the study you are reviewing? What were the authors trying to discover?
• Was the research funded by a source that could influence the findings?
• What were the research methodologies? Analyze its literature review, the samples and variables used, the results, and the conclusions.
• Does the research seem to be complete? Could it have been conducted more soundly? What further questions does it raise?
• If there are conflicting studies, why do you think that is?
• How are the authors viewed in the field? Has this study been cited? If so, how has it been analyzed?

Tips: 

• Review the abstracts carefully.  
• Keep careful notes so that you may track your thought processes during the research process.
• Create a matrix of the studies for easy analysis, and synthesis, across all of the studies.
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What is a literature review? [with examples]

What is a literature review?

The purpose of a literature review, how to write a literature review, the format of a literature review, general formatting rules, the length of a literature review, literature review examples, frequently asked questions about literature reviews, related articles.

A literature review is an assessment of the sources in a chosen topic of research.

In a literature review, you’re expected to report on the existing scholarly conversation, without adding new contributions.

If you are currently writing one, you've come to the right place. In the following paragraphs, we will explain:

• the objective of a literature review
• how to write a literature review
• the basic format of a literature review

Tip: It’s not always mandatory to add a literature review in a paper. Theses and dissertations often include them, whereas research papers may not. Make sure to consult with your instructor for exact requirements.

The four main objectives of a literature review are:

• Studying the references of your research area
• Summarizing the main arguments
• Identifying current gaps, stances, and issues
• Presenting all of the above in a text

Ultimately, the main goal of a literature review is to provide the researcher with sufficient knowledge about the topic in question so that they can eventually make an intervention.

The format of a literature review is fairly standard. It includes an:

• introduction that briefly introduces the main topic
• body that includes the main discussion of the key arguments
• conclusion that highlights the gaps and issues of the literature

➡️ Take a look at our guide on how to write a literature review to learn more about how to structure a literature review.

First of all, a literature review should have its own labeled section. You should indicate clearly in the table of contents where the literature can be found, and you should label this section as “Literature Review.”

➡️ For more information on writing a thesis, visit our guide on how to structure a thesis .

There is no set amount of words for a literature review, so the length depends on the research. If you are working with a large amount of sources, it will be long. If your paper does not depend entirely on references, it will be short.

Take a look at these three theses featuring great literature reviews:

• School-Based Speech-Language Pathologist's Perceptions of Sensory Food Aversions in Children [ PDF , see page 20]
• Who's Writing What We Read: Authorship in Criminological Research [ PDF , see page 4]
• A Phenomenological Study of the Lived Experience of Online Instructors of Theological Reflection at Christian Institutions Accredited by the Association of Theological Schools [ PDF , see page 56]

Literature reviews are most commonly found in theses and dissertations. However, you find them in research papers as well.

There is no set amount of words for a literature review, so the length depends on the research. If you are working with a large amount of sources, then it will be long. If your paper does not depend entirely on references, then it will be short.

No. A literature review should have its own independent section. You should indicate clearly in the table of contents where the literature review can be found, and label this section as “Literature Review.”

The main goal of a literature review is to provide the researcher with sufficient knowledge about the topic in question so that they can eventually make an intervention.

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Introduction to Literature Reviews

Introduction.

• Step One: Define
• Step Two: Research
• Step Three: Write
• Suggested Readings

A literature review is a written work that :

• Compiles significant research published on a topic by accredited scholars and researchers;
• —Surveys scholarly articles, books, dissertations, conference proceedings, and other sources;
• —Examines contrasting perspectives, theoretical approaches, methodologies, findings, results, conclusions.
• —Reviews critically, analyzes, and synthesizes existing research on a topic; and,
• Performs a thorough “re” view, “overview”, or “look again” of past and current works on a subject, issue, or theory.

From these analyses, the writer then offers an overview of the current status of a particular area of knowledge from both a practical and theoretical perspective.

Literature reviews are important because they are usually a  required  step in a thesis proposal (Master's or PhD). The proposal will not be well-supported without a literature review. Also, literature reviews are important because they help you learn important authors and ideas in your field. This is useful for your coursework and your writing. Knowing key authors also helps you become acquainted with other researchers in your field.

Look at this diagram and imagine that your research is the "something new." This shows how your research should relate to major works and other sources.

Olivia Whitfield | Graduate Reference Assistant | 2012-2015

• Next: Step One: Define >>
• Last Updated: Jun 28, 2023 5:49 PM
• URL: https://libraryguides.missouri.edu/literaturereview

• University of Texas Libraries

Literature Reviews

• What is a literature review?
• Steps in the Literature Review Process
• Define your research question
• Determine inclusion and exclusion criteria
• Choose databases and search
• Review Results
• Synthesize Results
• Analyze Results
• Librarian Support
• Artificial Intelligence (AI) Tools

What is a Literature Review?

A literature or narrative review is a comprehensive review and analysis of the published literature on a specific topic or research question. The literature that is reviewed contains: books, articles, academic articles, conference proceedings, association papers, and dissertations. It contains the most pertinent studies and points to important past and current research and practices. It provides background and context, and shows how your research will contribute to the field. 

A literature review should: 

• Provide a comprehensive and updated review of the literature;
• Explain why this review has taken place;
• Articulate a position or hypothesis;
• Acknowledge and account for conflicting and corroborating points of view

From  S age Research Methods

Purpose of a Literature Review

A literature review can be written as an introduction to a study to:

• Demonstrate how a study fills a gap in research
• Compare a study with other research that's been done

Or it can be a separate work (a research article on its own) which:

• Organizes or describes a topic
• Describes variables within a particular issue/problem

Limitations of a Literature Review

Some of the limitations of a literature review are:

• It's a snapshot in time. Unlike other reviews, this one has beginning, a middle and an end. There may be future developments that could make your work less relevant.
• It may be too focused. Some niche studies may miss the bigger picture.
• It can be difficult to be comprehensive. There is no way to make sure all the literature on a topic was considered.
• It is easy to be biased if you stick to top tier journals. There may be other places where people are publishing exemplary research. Look to open access publications and conferences to reflect a more inclusive collection. Also, make sure to include opposing views (and not just supporting evidence).

Source: Grant, Maria J., and Andrew Booth. “A Typology of Reviews: An Analysis of 14 Review Types and Associated Methodologies.” Health Information & Libraries Journal, vol. 26, no. 2, June 2009, pp. 91–108. Wiley Online Library, doi:10.1111/j.1471-1842.2009.00848.x.

Meryl Brodsky : Communication and Information Studies

Hannah Chapman Tripp : Biology, Neuroscience

Carolyn Cunningham : Human Development & Family Sciences, Psychology, Sociology

Larayne Dallas : Engineering

Janelle Hedstrom : Special Education, Curriculum & Instruction, Ed Leadership & Policy ​

Susan Macicak : Linguistics

Imelda Vetter : Dell Medical School

For help in other subject areas, please see the guide to library specialists by subject .

Periodically, UT Libraries runs a workshop covering the basics and library support for literature reviews. While we try to offer these once per academic year, we find providing the recording to be helpful to community members who have missed the session. Following is the most recent recording of the workshop, Conducting a Literature Review. To view the recording, a UT login is required.

• October 26, 2022 recording
• Last Updated: Jun 18, 2024 1:00 PM
• URL: https://guides.lib.utexas.edu/literaturereviews

Libraries | Research Guides

Literature reviews, what is a literature review, learning more about how to do a literature review.

• Planning the Review
• The Research Question
• Choosing Where to Search
• Organizing the Review
• Writing the Review

A literature review is a review and synthesis of existing research on a topic or research question. A literature review is meant to analyze the scholarly literature, make connections across writings and identify strengths, weaknesses, trends, and missing conversations. A literature review should address different aspects of a topic as it relates to your research question. A literature review goes beyond a description or summary of the literature you have read. 

• Sage Research Methods Core Collection This link opens in a new window SAGE Research Methods supports research at all levels by providing material to guide users through every step of the research process. SAGE Research Methods is the ultimate methods library with more than 1000 books, reference works, journal articles, and instructional videos by world-leading academics from across the social sciences, including the largest collection of qualitative methods books available online from any scholarly publisher. – Publisher

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• Last Updated: May 2, 2024 10:39 AM
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Literature review

A general guide on how to conduct and write a literature review.

Please check course or programme information and materials provided by teaching staff, including your project supervisor, for subject-specific guidance.

What is a literature review?

A literature review is a piece of academic writing demonstrating knowledge and understanding of the academic literature on a specific topic placed in context.  A literature review also includes a critical evaluation of the material; this is why it is called a literature review rather than a literature report. It is a process of reviewing the literature, as well as a form of writing.

To illustrate the difference between reporting and reviewing, think about television or film review articles.  These articles include content such as a brief synopsis or the key points of the film or programme plus the critic’s own evaluation.  Similarly the two main objectives of a literature review are firstly the content covering existing research, theories and evidence, and secondly your own critical evaluation and discussion of this content. 

Usually a literature review forms a section or part of a dissertation, research project or long essay.  However, it can also be set and assessed as a standalone piece of work.

What is the purpose of a literature review?

…your task is to build an argument, not a library. Rudestam, K.E. and Newton, R.R. (1992) Surviving your dissertation: A comprehensive guide to content and process. California: Sage, p49.

In a larger piece of written work, such as a dissertation or project, a literature review is usually one of the first tasks carried out after deciding on a topic.  Reading combined with critical analysis can help to refine a topic and frame research questions.  Conducting a literature review establishes your familiarity with and understanding of current research in a particular field before carrying out a new investigation. After doing a literature review, you should know what research has already been done and be able to identify what is unknown within your topic.

When doing and writing a literature review, it is good practice to:

• summarise and analyse previous research and theories;
• identify areas of controversy and contested claims;
• highlight any gaps that may exist in research to date.

Conducting a literature review

Focusing on different aspects of your literature review can be useful to help plan, develop, refine and write it.  You can use and adapt the prompt questions in our worksheet below at different points in the process of researching and writing your review.  These are suggestions to get you thinking and writing.

Developing and refining your literature review (pdf)

Developing and refining your literature review (Word)

Developing and refining your literature review (Word rtf)

Writing a literature review has a lot in common with other assignment tasks.  There is advice on our other pages about thinking critically, reading strategies and academic writing.  Our literature review top tips suggest some specific things you can do to help you submit a successful review.

Literature review top tips (pdf)

Literature review top tips (Word rtf)

Our reading page includes strategies and advice on using books and articles and a notes record sheet grid you can use.

Reading at university

The Academic writing page suggests ways to organise and structure information from a range of sources and how you can develop your argument as you read and write.

Academic writing

The Critical thinking page has advice on how to be a more critical researcher and a form you can use to help you think and break down the stages of developing your argument.

Critical thinking

As with other forms of academic writing, your literature review needs to demonstrate good academic practice by following the Code of Student Conduct and acknowledging the work of others through citing and referencing your sources.  

Good academic practice

As with any writing task, you will need to review, edit and rewrite sections of your literature review.  The Editing and proofreading page includes tips on how to do this and strategies for standing back and thinking about your structure and checking the flow of your argument.

Editing and proofreading

Guidance on literature searching from the University Library

The Academic Support Librarians have developed LibSmart I and II, Learn courses to help you develop and enhance your digital research skills and capabilities; from getting started with the Library to managing data for your dissertation.

Searching using the library’s DiscoverEd tool: DiscoverEd

Finding resources in your subject: Subject guides

The Academic Support Librarians also provide one-to-one appointments to help you develop your research strategies.

1 to 1 support for literature searching and systematic reviews

Advice to help you optimise use of Google Scholar, Google Books and Google for your research and study: Using Google

Managing and curating your references

A referencing management tool can help you to collect and organise and your source material to produce a bibliography or reference list. 

Referencing and reference management

Information Services provide access to Cite them right online which is a guide to the main referencing systems and tells you how to reference just about any source (EASE log-in may be required).

Cite them right

Published study guides

There are a number of scholarship skills books and guides available which can help with writing a literature review.  Our Resource List of study skills guides includes sections on Referencing, Dissertation and project writing and Literature reviews.

Study skills guides

This article was published on 2024-02-26

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Home » Literature Review – Types Writing Guide and Examples

Literature Review – Types Writing Guide and Examples

Table of Contents

Literature Review

Definition:

A literature review is a comprehensive and critical analysis of the existing literature on a particular topic or research question. It involves identifying, evaluating, and synthesizing relevant literature, including scholarly articles, books, and other sources, to provide a summary and critical assessment of what is known about the topic.

Types of Literature Review

Types of Literature Review are as follows:

• Narrative literature review : This type of review involves a comprehensive summary and critical analysis of the available literature on a particular topic or research question. It is often used as an introductory section of a research paper.
• Systematic literature review: This is a rigorous and structured review that follows a pre-defined protocol to identify, evaluate, and synthesize all relevant studies on a specific research question. It is often used in evidence-based practice and systematic reviews.
• Meta-analysis: This is a quantitative review that uses statistical methods to combine data from multiple studies to derive a summary effect size. It provides a more precise estimate of the overall effect than any individual study.
• Scoping review: This is a preliminary review that aims to map the existing literature on a broad topic area to identify research gaps and areas for further investigation.
• Critical literature review : This type of review evaluates the strengths and weaknesses of the existing literature on a particular topic or research question. It aims to provide a critical analysis of the literature and identify areas where further research is needed.
• Conceptual literature review: This review synthesizes and integrates theories and concepts from multiple sources to provide a new perspective on a particular topic. It aims to provide a theoretical framework for understanding a particular research question.
• Rapid literature review: This is a quick review that provides a snapshot of the current state of knowledge on a specific research question or topic. It is often used when time and resources are limited.
• Thematic literature review : This review identifies and analyzes common themes and patterns across a body of literature on a particular topic. It aims to provide a comprehensive overview of the literature and identify key themes and concepts.
• Realist literature review: This review is often used in social science research and aims to identify how and why certain interventions work in certain contexts. It takes into account the context and complexities of real-world situations.
• State-of-the-art literature review : This type of review provides an overview of the current state of knowledge in a particular field, highlighting the most recent and relevant research. It is often used in fields where knowledge is rapidly evolving, such as technology or medicine.
• Integrative literature review: This type of review synthesizes and integrates findings from multiple studies on a particular topic to identify patterns, themes, and gaps in the literature. It aims to provide a comprehensive understanding of the current state of knowledge on a particular topic.
• Umbrella literature review : This review is used to provide a broad overview of a large and diverse body of literature on a particular topic. It aims to identify common themes and patterns across different areas of research.
• Historical literature review: This type of review examines the historical development of research on a particular topic or research question. It aims to provide a historical context for understanding the current state of knowledge on a particular topic.
• Problem-oriented literature review : This review focuses on a specific problem or issue and examines the literature to identify potential solutions or interventions. It aims to provide practical recommendations for addressing a particular problem or issue.
• Mixed-methods literature review : This type of review combines quantitative and qualitative methods to synthesize and analyze the available literature on a particular topic. It aims to provide a more comprehensive understanding of the research question by combining different types of evidence.

Parts of Literature Review

Parts of a literature review are as follows:

Introduction

The introduction of a literature review typically provides background information on the research topic and why it is important. It outlines the objectives of the review, the research question or hypothesis, and the scope of the review.

Literature Search

This section outlines the search strategy and databases used to identify relevant literature. The search terms used, inclusion and exclusion criteria, and any limitations of the search are described.

Literature Analysis

The literature analysis is the main body of the literature review. This section summarizes and synthesizes the literature that is relevant to the research question or hypothesis. The review should be organized thematically, chronologically, or by methodology, depending on the research objectives.

Critical Evaluation

Critical evaluation involves assessing the quality and validity of the literature. This includes evaluating the reliability and validity of the studies reviewed, the methodology used, and the strength of the evidence.

The conclusion of the literature review should summarize the main findings, identify any gaps in the literature, and suggest areas for future research. It should also reiterate the importance of the research question or hypothesis and the contribution of the literature review to the overall research project.

The references list includes all the sources cited in the literature review, and follows a specific referencing style (e.g., APA, MLA, Harvard).

How to write Literature Review

Here are some steps to follow when writing a literature review:

• Define your research question or topic : Before starting your literature review, it is essential to define your research question or topic. This will help you identify relevant literature and determine the scope of your review.
• Conduct a comprehensive search: Use databases and search engines to find relevant literature. Look for peer-reviewed articles, books, and other academic sources that are relevant to your research question or topic.
• Evaluate the sources: Once you have found potential sources, evaluate them critically to determine their relevance, credibility, and quality. Look for recent publications, reputable authors, and reliable sources of data and evidence.
• Organize your sources: Group the sources by theme, method, or research question. This will help you identify similarities and differences among the literature, and provide a structure for your literature review.
• Analyze and synthesize the literature : Analyze each source in depth, identifying the key findings, methodologies, and conclusions. Then, synthesize the information from the sources, identifying patterns and themes in the literature.
• Write the literature review : Start with an introduction that provides an overview of the topic and the purpose of the literature review. Then, organize the literature according to your chosen structure, and analyze and synthesize the sources. Finally, provide a conclusion that summarizes the key findings of the literature review, identifies gaps in knowledge, and suggests areas for future research.
• Edit and proofread: Once you have written your literature review, edit and proofread it carefully to ensure that it is well-organized, clear, and concise.

Examples of Literature Review

Here’s an example of how a literature review can be conducted for a thesis on the topic of “ The Impact of Social Media on Teenagers’ Mental Health”:

• Start by identifying the key terms related to your research topic. In this case, the key terms are “social media,” “teenagers,” and “mental health.”
• Use academic databases like Google Scholar, JSTOR, or PubMed to search for relevant articles, books, and other publications. Use these keywords in your search to narrow down your results.
• Evaluate the sources you find to determine if they are relevant to your research question. You may want to consider the publication date, author’s credentials, and the journal or book publisher.
• Begin reading and taking notes on each source, paying attention to key findings, methodologies used, and any gaps in the research.
• Organize your findings into themes or categories. For example, you might categorize your sources into those that examine the impact of social media on self-esteem, those that explore the effects of cyberbullying, and those that investigate the relationship between social media use and depression.
• Synthesize your findings by summarizing the key themes and highlighting any gaps or inconsistencies in the research. Identify areas where further research is needed.
• Use your literature review to inform your research questions and hypotheses for your thesis.

For example, after conducting a literature review on the impact of social media on teenagers’ mental health, a thesis might look like this:

“Using a mixed-methods approach, this study aims to investigate the relationship between social media use and mental health outcomes in teenagers. Specifically, the study will examine the effects of cyberbullying, social comparison, and excessive social media use on self-esteem, anxiety, and depression. Through an analysis of survey data and qualitative interviews with teenagers, the study will provide insight into the complex relationship between social media use and mental health outcomes, and identify strategies for promoting positive mental health outcomes in young people.”

Reference: Smith, J., Jones, M., & Lee, S. (2019). The effects of social media use on adolescent mental health: A systematic review. Journal of Adolescent Health, 65(2), 154-165. doi:10.1016/j.jadohealth.2019.03.024

Reference Example: Author, A. A., Author, B. B., & Author, C. C. (Year). Title of article. Title of Journal, volume number(issue number), page range. doi:0000000/000000000000 or URL

Applications of Literature Review

some applications of literature review in different fields:

• Social Sciences: In social sciences, literature reviews are used to identify gaps in existing research, to develop research questions, and to provide a theoretical framework for research. Literature reviews are commonly used in fields such as sociology, psychology, anthropology, and political science.
• Natural Sciences: In natural sciences, literature reviews are used to summarize and evaluate the current state of knowledge in a particular field or subfield. Literature reviews can help researchers identify areas where more research is needed and provide insights into the latest developments in a particular field. Fields such as biology, chemistry, and physics commonly use literature reviews.
• Health Sciences: In health sciences, literature reviews are used to evaluate the effectiveness of treatments, identify best practices, and determine areas where more research is needed. Literature reviews are commonly used in fields such as medicine, nursing, and public health.
• Humanities: In humanities, literature reviews are used to identify gaps in existing knowledge, develop new interpretations of texts or cultural artifacts, and provide a theoretical framework for research. Literature reviews are commonly used in fields such as history, literary studies, and philosophy.

Role of Literature Review in Research

Here are some applications of literature review in research:

• Identifying Research Gaps : Literature review helps researchers identify gaps in existing research and literature related to their research question. This allows them to develop new research questions and hypotheses to fill those gaps.
• Developing Theoretical Framework: Literature review helps researchers develop a theoretical framework for their research. By analyzing and synthesizing existing literature, researchers can identify the key concepts, theories, and models that are relevant to their research.
• Selecting Research Methods : Literature review helps researchers select appropriate research methods and techniques based on previous research. It also helps researchers to identify potential biases or limitations of certain methods and techniques.
• Data Collection and Analysis: Literature review helps researchers in data collection and analysis by providing a foundation for the development of data collection instruments and methods. It also helps researchers to identify relevant data sources and identify potential data analysis techniques.
• Communicating Results: Literature review helps researchers to communicate their results effectively by providing a context for their research. It also helps to justify the significance of their findings in relation to existing research and literature.

Purpose of Literature Review

Some of the specific purposes of a literature review are as follows:

• To provide context: A literature review helps to provide context for your research by situating it within the broader body of literature on the topic.
• To identify gaps and inconsistencies: A literature review helps to identify areas where further research is needed or where there are inconsistencies in the existing literature.
• To synthesize information: A literature review helps to synthesize the information from multiple sources and present a coherent and comprehensive picture of the current state of knowledge on the topic.
• To identify key concepts and theories : A literature review helps to identify key concepts and theories that are relevant to your research question and provide a theoretical framework for your study.
• To inform research design: A literature review can inform the design of your research study by identifying appropriate research methods, data sources, and research questions.

Characteristics of Literature Review

Some Characteristics of Literature Review are as follows:

• Identifying gaps in knowledge: A literature review helps to identify gaps in the existing knowledge and research on a specific topic or research question. By analyzing and synthesizing the literature, you can identify areas where further research is needed and where new insights can be gained.
• Establishing the significance of your research: A literature review helps to establish the significance of your own research by placing it in the context of existing research. By demonstrating the relevance of your research to the existing literature, you can establish its importance and value.
• Informing research design and methodology : A literature review helps to inform research design and methodology by identifying the most appropriate research methods, techniques, and instruments. By reviewing the literature, you can identify the strengths and limitations of different research methods and techniques, and select the most appropriate ones for your own research.
• Supporting arguments and claims: A literature review provides evidence to support arguments and claims made in academic writing. By citing and analyzing the literature, you can provide a solid foundation for your own arguments and claims.
• I dentifying potential collaborators and mentors: A literature review can help identify potential collaborators and mentors by identifying researchers and practitioners who are working on related topics or using similar methods. By building relationships with these individuals, you can gain valuable insights and support for your own research and practice.
• Keeping up-to-date with the latest research : A literature review helps to keep you up-to-date with the latest research on a specific topic or research question. By regularly reviewing the literature, you can stay informed about the latest findings and developments in your field.

Advantages of Literature Review

There are several advantages to conducting a literature review as part of a research project, including:

• Establishing the significance of the research : A literature review helps to establish the significance of the research by demonstrating the gap or problem in the existing literature that the study aims to address.
• Identifying key concepts and theories: A literature review can help to identify key concepts and theories that are relevant to the research question, and provide a theoretical framework for the study.
• Supporting the research methodology : A literature review can inform the research methodology by identifying appropriate research methods, data sources, and research questions.
• Providing a comprehensive overview of the literature : A literature review provides a comprehensive overview of the current state of knowledge on a topic, allowing the researcher to identify key themes, debates, and areas of agreement or disagreement.
• Identifying potential research questions: A literature review can help to identify potential research questions and areas for further investigation.
• Avoiding duplication of research: A literature review can help to avoid duplication of research by identifying what has already been done on a topic, and what remains to be done.
• Enhancing the credibility of the research : A literature review helps to enhance the credibility of the research by demonstrating the researcher’s knowledge of the existing literature and their ability to situate their research within a broader context.

Limitations of Literature Review

Limitations of Literature Review are as follows:

• Limited scope : Literature reviews can only cover the existing literature on a particular topic, which may be limited in scope or depth.
• Publication bias : Literature reviews may be influenced by publication bias, which occurs when researchers are more likely to publish positive results than negative ones. This can lead to an incomplete or biased picture of the literature.
• Quality of sources : The quality of the literature reviewed can vary widely, and not all sources may be reliable or valid.
• Time-limited: Literature reviews can become quickly outdated as new research is published, making it difficult to keep up with the latest developments in a field.
• Subjective interpretation : Literature reviews can be subjective, and the interpretation of the findings can vary depending on the researcher’s perspective or bias.
• Lack of original data : Literature reviews do not generate new data, but rather rely on the analysis of existing studies.
• Risk of plagiarism: It is important to ensure that literature reviews do not inadvertently contain plagiarism, which can occur when researchers use the work of others without proper attribution.

About the author

Muhammad Hassan

Researcher, Academic Writer, Web developer

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• Study Protocol
• Open access
• Published: 04 July 2024

Adherence to single inhaler triple therapy and digital inhalers in Chronic Obstructive Pulmonary Disease: a literature review and protocol for a randomized controlled trial (TRICOLON study)

• Liz J. A. Cuperus 1 , 2 , 3 ,
• Job van der Palen 4 ,
• Arnoud Aldenkamp 5 ,
• Astrid van Huisstede 6 ,
• Erik W. M. A. Bischoff 7 ,
• Job F. M. van Boven 8 ,
• Folkert Brijker 9 ,
• Stephan Dik 10 ,
• Jeroen A. J. M. van Excel 11 ,
• Martijn Goosens 12 ,
• Peter Th. W. van Hal 13 ,
• Jolanda C. Kuijvenhoven 14 ,
• Lisette I. Z. Kunz 15 ,
• Erwin C. Vasbinder 16 ,
• Huib A. M. Kerstjens 2 ,
• Johannes C. C. M. in ’t Veen 1 , 3 &

the TRICOLON study group

BMC Pulmonary Medicine volume  24 , Article number:  317 ( 2024 ) Cite this article

Metrics details

Medication non-adherence is a significant problem in patients with Chronic Obstructive Pulmonary Disease (COPD). Efforts to address this issue are receiving increased attention. Simplifying treatment by prescribing single-inhaler triple therapy (SITT) as an alternative to multi-inhaler triple therapy (MITT) or with smart inhalers are often considered potential solutions. However, the actual impact of these innovations on adherence and clinical outcomes is unclear.

To address this knowledge gap we first conducted a literature review focusing on two research questions: 1) the difference in adherence between SITT and MITT users in COPD, and 2) the effect of smart inhalers on adherence in COPD. Separate searches were conducted in PubMed and two authors independently assessed the articles. In addition, we present a protocol for a study to acquire knowledge for the gaps identified.

To address the first research question, 8 trials were selected for further review. All trials were observational, i.e. randomized controlled trials were lacking. Seven of these trials showed higher adherence and/or persistence in patients on SITT compared with patients on MITT. In addition, four studies showed a positive effect of SITT on various clinical outcomes. For the second research question, 11 trials were selected for review. While most of the studies showed a positive effect of smart inhalers on adherence, there was considerable variation in the results regarding their effect on other clinical outcomes.

The TRICOLON (TRIple therapy COnvenience by the use of one or multipLe Inhalers and digital support in ChrONic Obstructive Pulmonary Disease) trial aims to improve understanding regarding the effectiveness of SITT and smart inhalers in enhancing adherence. This open-label, randomized, multi-center study will enroll COPD patients requiring triple therapy at ten participating hospitals. In total, 300 patients will be randomized into three groups: 1) MITT; 2) SITT; 3) SITT with digital support through a smart inhaler and an e-health platform. The follow-up period will be one year, during which three methods of measuring adherence will be used: smart inhaler data, self-reported data using the Test of Adherence to Inhalers (TAI) questionnaire, and drug analysis in scalp hair samples. Finally, differences in clinical outcomes between the study groups will be compared.

Our review suggests promising results concerning the effect of SITT, as opposed to MITT, and smart inhalers on adherence. However, the quality of evidence is limited due to the absence of randomized controlled trials and/or the short duration of follow-up in many studies. Moreover, its impact on clinical outcomes shows considerable variation. The TRICOLON trial aims to provide solid data on these frequently mentioned solutions to non-adherence in COPD. Collecting data in a well-designed randomized controlled trial is challenging, but the design of this trial addresses both the usefulness of SITT and smart inhalers while ensuring minimal interference in participants' daily lives.

Trial registration

NCT05495698 (Clinicaltrials.gov), registered at 08–08-2022. Protocol version: version 5, date 27–02-2023.

Peer Review reports

Introduction

Chronic obstructive pulmonary disease (COPD) is characterized by chronic respiratory symptoms due to abnormalities in the airways and/or alveoli, resulting in persistent and often progressive airflow obstruction. Inhalation medication is the primary medical treatment, with three types of inhalation medication available as maintenance therapy: 1) long-acting β2-agonist (LABA), 2) long-acting muscarinic antagonist (LAMA), and 3) inhaled corticosteroids (ICS). Triple therapy is defined as treatment with LABA, LAMA and ICS [ 1 ]. Large randomized controlled trials have shown that triple therapy provides clinical benefits compared to dual therapy in patients with moderate-to-severe COPD and a history of exacerbations, particularly when eosinophilia is present [ 2 , 3 , 4 , 5 , 6 ]. Furthermore, two trials suggest that triple therapy reduces mortality in this specific population [ 7 , 8 ]. Triple therapy can be administered through multiple devices, known as multi-inhaler-triple therapy (MITT), or combined in one inhaler, known as single-inhaler-triple therapy (SITT). Assessment of adherence to inhalation therapy is a crucial element in managing COPD patients according to the Global Initiative for Chronic Obstructive Lung Disease (GOLD) [ 1 ]. Previous studies have shown that medication adherence is poor in patients with COPD. A systematic review showed that non-adherence rates ranged from 22 to 93%, depending on the study population and method of measurement [ 9 ]. Non-adherence is associated with poor clinical and economic outcomes [ 10 , 11 ]. Simplifying treatment with smart-inhalers and prescribing single-inhaler triple therapy (SITT) as an alternative to multi-inhaler triple therapy (MITT) can be considered as potential solutions. Nowadays, the GOLD report (version 2024) acknowledges that a single inhaler may be more convenient compared to multi-inhaler therapy. [ 1 ]. The actual impact of these innovations on adherence is unclear. Therefore, we conducted a literature review to examine the current evidence on these two potential solutions. Should the evidence prove to be insufficient, we wanted to present a protocol for a study to fill this gap.

Methods for measuring adherence

Adherence is defined as the process by which patients take their medication as prescribed, while persistence refers to the duration from initiation to discontinuation of the treatment. Adherence and persistence are complex constructs, as previously described by Vrijens et al. [ 12 , 13 ]. Various methods can be used to assess medication adherence. Healthcare professionals commonly inquire directly about their patients' adherence. While this approach is straightforward, research has demonstrated its unreliability in comparison to more objective measurement methods. Unstructured self-reports often lead to an overestimation of adherence [ 14 ]. Patients can structurally self-report their adherence using questionnaires, such as the Test of Adherence to Inhalers (TAI). The TAI is developed specifically to measure adherence to inhalation medication in patients with COPD or asthma [ 15 ]. Furthermore, pharmacy data are often used to determine patient’s access to medication over time by calculating the Proportion of Days Covered (PDC). This method may be less reliable due to missing or inaccessible data (e.g. when multiple pharmacies are used) and the uncertainty about whether the patient actually used the medication [ 16 , 17 ]. Smart inhalers offer a more objective method for measuring adherence. These electronic sensors (e-devices) are attached to or integrated into inhalers. Devices range from simple dose counters to advanced devices that provide reminders, feedback, and/or analyse inhalation technique [ 18 ]. Smart inhalers are often integrated with other e-health interventions, such as telemonitoring, personalised feedback with apps, counselling, and training [ 19 , 20 , 21 ]. Finally, hair analysis can provide a bioanalytical assessment of average long-term drug exposure in the human body. This method could potentially provide an objective measure of adherence over the last few months. However, external factors can impact measurement, and only small part of medication that has been present in the systemic blood circulation is built into hair [ 22 ].

First, we present a review of the literature on two strategies to improve adherence. Second, we describe the study protocol of the TRICOLON trial (TRIple therapy COnvenience by the use of one or multipLe Inhalers and digital support in ChrONic Obstructive Pulmonary Disease).

Search strategy literature review

Separate searches were conducted in PubMed based on two research questions: 1) What is the difference in adherence between SITT and MITT users in COPD?, and 2) What is the effect of smart inhalers on adherence in COPD? The selection of articles from the second PubMed search was supplemented by four papers known to the authors or found by snowballing. Two authors independently assessed these articles to determine whether they should be included in this review (LC and JiV). In cases of disagreement, the opinion of a third author was sought (HK). Only original English-language studies were included. Details of the PubMed search and selection process can be found in the Appendix, Suppl.1.

Assessment of the evidence

The primary outcome was the adherence and/or persistence to triple therapy. Secondary outcomes were clinical outcomes, such as exacerbations, COPD Assessment Test (CAT) score, and FEV 1 . Each study underwent an evaluation across multiple criteria to assess the evidence supporting the research question. The strength of the study design was rated with stars: one star for retrospective studies, two stars for prospective observational studies or intervention studies without randomization (e.g. before-and-after designs), and three stars for randomised controlled trials. A green smiley indicates statistically significant superior results in the intervention group (either SITT or smart-inhaler group, depending on the research question) compared to the control group; a yellow neutral smiley signifies no difference between the groups, while a red sad smiley denotes statistically significant inferior results in the intervention group compared to the control group. Additionally, a thumbs-up signifies that other clinical outcomes were measured in that study, whereas a thumbs-down indicates the absence of measurements for other clinical outcomes, Tables  1 and  2 .

Literature review

Adherence to single versus multi inhaler triple therapy.

The first search yielded eighteen articles, Suppl. Figure 1. After the selection process, eight articles were included for further evaluation, Table  1 . None had a randomized controlled design. Four studies compared SITT with MITT in a prospective setting [ 23 , 27 , 28 , 30 ] and four in a retrospective analysis [ 24 , 25 , 26 , 29 ]. The retrospective studies used either anonymized data from electronic health records of patients in primary or secondary care [ 24 , 26 ], or databases of health insurance claims [ 25 , 29 ]. Seven of these studies showed that adherence and/or persistence to SITT was significantly higher compared to MITT in COPD patients [ 23 , 24 , 25 , 27 , 28 , 29 , 30 ]. Deslee et al. presented contrasting findings, showing that while persistence was higher in the SITT group (median 181 versus 135 days), adherence levels were similar in SITT and MITT (85.7% versus 86.1%) [ 26 ]. The seven trials that showed a positive effect of SITT on adherence were heterogeneous in terms of study design, and methods of measurement, type of inhaler, and molecules. Although most studies directly compared SITT with MITT, two of the prospective studies assessed adherence to SITT after switching from either dual therapy or MITT [ 27 , 28 ]. Brusselle et al. reported separate results for former MITT users: 71.9% at baseline, 74.7% three months after switching to SITT, and 83.8% at six months [ 28 ]. In contrast, Gessner et al. did not report separate results for the different treatments at baseline. Therefore, this difference between SITT and the control group should be interpreted with caution [ 27 ].

Clinical outcomes in single vs multi inhaler triple therapy

Five trials investigated the effect of SITT compared to MITT on clinical outcomes. Four of these trials showed a beneficial effect of SITT on clinical outcomes, Table  1 . SITT users had a lower risk of exacerbations compared to MITT users in two studies [ 23 , 28 ]; three studies showed lower CAT-scores and higher FEV 1 in SITT users [ 27 , 28 , 30 ]; and one study showed a reduced all-cause mortality risk in SITT users [HR: 0.475 (0.237–0.952), p  = 0.036] [ 23 ]. In contrast to these studies with positive effects of SITT, Bogart et al. showed different results in two different groups of patients. In patients enrolled in Medicare Advantage with Part D (MAPD) insurance, a significant reduction in exacerbations and healthcare utilisation was seen in the SITT group. However, these differences were not statistically significant in the commercially insured patients [ 29 ].

The effect of smart inhalers on adherence

The second part of our literature review investigated the effect of smart inhalers on adherence in patients with COPD and resulted in 78 articles, from which 11 studies were selected, Table  2 . These studies were heterogenetic in terms of number of patients, study design, and type of intervention and/or smart inhaler. Additionally, length of follow-up ranged from 1 to 12 months, with the vast majority (90.9%) having a follow-up period of ≤ 6 months. Seven studies prospectively compared COPD patients who used a smart-inhalers with a control group; four of those had a randomized controlled open-label design. Six of these seven studies showed a statistically better adherence in the intervention group [ 19 , 31 , 32 , 37 , 38 , 40 ]; one prospective study showed no difference in adherence between smart inhaler users and controls [ 33 ]. Four other observational studies showed variable average adherence rates in smart-inhaler users from 44–77%; however, it should be noted that these trials did not include a control group without smart-inhaler [ 34 , 35 , 36 , 39 ].

The effect of smart inhalers on clinical outcomes

Nine studies also investigated the effect of smart inhalers on clinical outcomes [ 19 , 31 , 32 , 33 , 35 , 36 , 37 , 38 , 39 ]. These studies showed mixed results, Table  2 . A significant better inhalation technique was seen in two studies [ 31 , 33 ]. The impact of smart inhalers on other clinical outcomes, including exacerbations, disease burden, quality of life assessments, rescue medication usage, hospitalizations, and healthcare utilization, varied across different studies [ 19 , 32 , 33 , 35 , 36 , 37 , 38 , 39 ].

Conclusion of literature review

This review suggests promising results concerning the effect of SITT, as opposed to MITT, and smart inhalers on adherence. However, the quality of evidence is limited due to the absence of randomized controlled trials and/or the short duration of follow-up in many studies. Moreover, there is considerable variation in the findings of these studies regarding diverse clinical outcomes. Consequently, there is a clear need for comprehensive randomised controlled trials to evaluate the benefits of SITT versus MITT in COPD, as well as the individual and combined effects of smart inhalers, both on adherence and clinical outcomes.

Study protocol for an RCT: the TRICOLON study

The TRICOLON study was initiated to provide evidence on two previously mentioned potential solutions for the non-adherence issue in COPD patients. The primary objective is to investigate whether the adherence to SITT is superior to the adherence to MITT over 12 months of treatment and to investigate whether the adherence of SITT users with a smart inhaler and digital support is superior to the adherence of MITT and SITT users without the smart inhaler and digital support. As a secondary objective, three methods of measuring adherence will be compared: smart inhaler data, self-reported data using the Test of Adherence to Inhalers (TAI) questionnaire [ 15 ], and drug analysis of formoterol in scalp hair samples [ 41 ]. Finally, differences in clinical outcomes between the study groups will be examined.

Study design

The TRICOLON study is an investigator-initiated, prospective, open-label, randomised, real-world, multicentre study. The study will be conducted at ten hospitals in the Netherlands, Supplement 2. Patients will be recruited from the pulmonary wards or outpatient clinics of the participating hospitals. Informed consent will be obtained by a member of the research team. Participants are randomly assigned in a 1:1:1 ratio to one of three groups: 1) multi-inhaler triple therapy (Bevespi® and Qvar®), 2) single-inhaler triple therapy (Trimbow®), 3) single-inhaler triple therapy (Trimbow®) with digital support, Fig.  1 . The follow-up period will be one year, during which we aim to minimise disruption to their usual care, thus creating a (close to) real-world situation. The study outline is presented in Fig.  2 . Ethical approval for this study was granted by the United Medical Research Ethics Committees (NL79938.100.22). The trial is registered on clinicaltrials.gov (NCT05495698).

Study design. Patients are randomly assigned in a 1:1:1 ratio to one of three groups: 1) multi-inhaler triple therapy (Bevespi® and Qvar®), 2) single-inhaler triple therapy (Trimbow®), 3) single-inhaler triple therapy (Trimbow®) with e-health. The follow-up period is one year

Study program

*time in months

Study participants

A total of 300 patients will be enrolled. Patients with a diagnosis of COPD and an indication for triple therapy according to their physician following the GOLD report are eligible to participate. Patients are excluded if asthma is the dominant diagnosis (asthma in the past or as a comorbidity is allowed), if patients use nebulizers or if they already use an e-health application for their COPD. The inclusion and exclusion criteria are displayed in Table  3 .

Interventions

The study groups have uniform doses, identical molecules and doses (beclomethasone 100µg, formoterol 6µg, and glycopyrronium 10µg), and the same device type (pressurised metered dose inhaler). Therefore, the only differentiating factors are the number of devices used and the use of digital support. Digital support comprises the Findair® smart-inhaler, an electronic device that is attached to the inhaler and measures the frequency and time of the actuations, and the Curavista® platform (Gezondheidsmeter PGO), a digital platform that promotes patient self-management by displaying their medication use and providing medication intake reminders [ 31 , 32 ]. Each patient is provided with smart inhalers that are attached to all their inhalers, including the potential rescue medication. This enables the measurement of actuation frequency and timing. The smart-inhalers are linked to the digital platform for data collection. However, it is important to note that only group 3 has access to an overview of the actuations with feedback in the app and reminders, along with full access to the digital platform. Groups 1 and 2 will not receive any reminders and cannot access the digital platform. Their e-health applications are solely used for data collection purposes, ensuring "silent monitoring" that should not influence their adherence.

We aim for all participants to complete the study using the original study medication. However, given the real-world nature of the study, it is possible that patients require a change in medication due to clinical reasons such as side effects or lack of effectiveness. To prevent the loss of these patients from the study, changes in medication are permitted only when absolutely necessary. Data collection will persist via the electronic devices and with the same settings of the app (silent monitoring or full access). Patients who no longer use a pressurized metered dose inhaler will be excluded, as the electronic devices are specifically tailored for this type of inhaler.

The primary outcome is the average adherence to ICS therapy (measured as the number of actuations registered by the smart-inhaler divided by the total number of doses prescribed, in %) over 12 months of treatment. As a secondary outcome, the average adherence to LABA/LAMA in study group 1 will be compared with adherence to ICS in group 1, and with adherence to LABA/LAMA/ICS in groups 2 and 3. Additional secondary outcomes include the percentage of patients with good adherence, defined as an average ICS adherence of more than 80% and less than 110% actuations measured by the smart inhaler; the Test of Adherence to Inhalers (TAI) scores; and drug levels of formoterol in scalp hair. The hair samples will be collected, stored, and prepared according to the guidelines of the Society of Hair Testing [ 42 ]. Additionally, the study will measure changes in Patient Reported Outcome Measures (PROMs), use of rescue medication, number of exacerbations and hospitalizations, healthcare consumption, and spirometry (FEV 1 ). The PROMs are displayed in Supplement 3.

Statistical analysis

The statistical software G*Power version 3.1.9.6 was used to calculate the sample size. The study aims to compare three groups: group 1 vs group 2, group 2 vs group 3, and group 1 vs group 3. The sample size calculation is based on the comparison of the average adherence in group 1 vs group 2 (so MITT vs SITT without e-health). Based on a previous study [ 19 ], we expect a 15% difference between the groups, with a standard deviation of 30%. The significance level of the test was set at (alpha) 0.0167 using the Holm-Bonferroni method to adjust for multiple testing, as we are comparing three groups (alpha 0.05/3 = 0.0167), with a power of 80%. We calculated n = 84 for each group using a two-sided T-test, and plan to include 100 patients in each group of the study, considering a potential drop-out rate of 15%. The patients will be randomized using the program Castor EDC. To prevent inequality in the study groups, at randomization patients will be stratified for their treatment before the study (dual therapy, MITT or SITT) and for inclusion during an exacerbation or during stable disease. The data will be analyzed using both the intention-to-treat (primary analysis) and per-protocol methods. The Kruskal–Wallis test or ANOVA, as appropriate, will be used to compare the average adherence between the three study groups. Post-hoc comparisons will be performed using Mann–Whitney U tests or Tukey’s HSD, as appropriate. The average baseline scores of the PROMs and baseline clinical status (FEV 1 , number of exacerbations, hospitalizations and rescue medication use) will be presented descriptively. These scores and outcomes are all continuous, unpaired data and will be compared between more than two groups. Therefore, we will use the Kruskal–Wallis or ANOVA, as appropriate, to investigate the differences between the three groups. The Net Promoter score is a binary variable, so we will use the Chi-square test. Questionnaire data will be analysed by both the difference in mean scores between groups and the percentage of patients achieving the minimally clinical important difference (MCID) when available. Furthermore, a mixed model repeated measurement analysis will be performed to assess the differences in the previously mentioned outcomes over time. The analysis will be conducted on normally distributed data, with or without transformations. The main parameter of interest is the group * time interaction. Between-group comparisons will be adjusted using the method of Sidak. If the data cannot be normalized, difference scores will be calculated (follow-up – baseline). These differences will be analysed using either the Kruskal–Wallis test or ANOVA, where appropriate. Post-hoc comparisons will be conducted using Mann–Whitney U tests or Tukey’s HSD, where appropriate.

Serious adverse events (SAEs) will be monitored and reported in accordance with the legal requirements and deadlines. The Ethics committee has granted permission for hospital admissions resulting from a COPD exacerbation not to be reported as SAE. This exemption is due to their frequent occurrence in this specific population. Instead, to monitor this fragile population, a Data and Safety Monitoring Board (DSMB) has been established. The DSMB will periodically review mortality rates, serious adverse events, and premature withdrawals from the study every six months. The application and e-health platform in use have a substantial history, spanning many years. Over the past two decades, 26 peer-reviewed scientific publications have been published. Notably, there have been no reported safety concerns, and assessments of usability, feasibility, and efficacy consistently yield positive results [ 43 ].

Non-adherence is a significant challenge in COPD patients, and addressing this issue is receiving increased attention. The first solution we investigated was simplifying the treatment by prescribing single-inhaler triple therapy (SITT) as an alternative to multi-inhaler triple therapy (MITT). The GOLD report 2023 suggested, for the first time, that single inhaler therapy may be more convenient than multi inhaler therapy [ 1 ]. However, although our literature review reveals some promising results regarding the effect of SITT on adherence, the quality of evidence is limited due to the absence of randomized controlled trials that specifically examined the difference in adherence between SITT and MITT. Due to the observational setting and design of all studies in the first part of this review, the SITT and MITT groups showed differences in their baseline characteristics, including the number of exacerbations prior to enrolment, disease severity, and FEV-1. Moreover, the quality of the observational data was occasionally limited. For example, two studies relied on administrative databases using health insurance claims [ 25 , 29 ]. Consequently, from these trials we are unable to draw conclusions on the cause-effect relationship between improved adherence and clinical outcomes. In contrast to the four studies included in our review, which all demonstrated slightly better clinical outcomes in SITT users, other literature, not incorporated into our review due to a lack of adherence as an outcome, presented contrasting results regarding the effect of SITT on clinical outcomes. Specifically, a retrospective study in Spain and an RCT showed improved clinical outcomes in SITT users [ 44 , 45 ]. However, three randomized controlled trials indicated that both SITT and MITT users exhibited similar results in terms of lung function, health status, exacerbation rate, and rescue medication usage [ 2 , 46 , 47 ].

The use of smart inhalers was the second potential solution to non-adherence that we investigated. Our review showed that while the effect on adherence was mostly positive, no consistent differences in clinical outcomes were observed. The strength of studies showing improved adherence in the absence of improved clinical outcomes is limited. These findings are consistent with other recent reviews in both COPD and asthma [ 18 , 20 , 21 ]. Demonstrating the connection between adherence and clinical outcomes has proven to be challenging. Given that COPD entails irreversible lung damage and the medication aims to stabilize rather than cure the disease, an extensive follow-up period is essential to demonstrate its impact on clinical outcomes. However, the current studies have limitations regarding the duration of follow-up. The smart inhalers used, as well as the supplementary interventions, and the extent of monitoring and/or interference varied significantly among the studies. The majority of smart inhalers used in current literature can only record the time and location of actuation. They are unable to measure whether inhalation is performed correctly. Other techniques, such as smart inhalers capable of measuring airflow or hair analysis of inhaled drugs, can assist in addressing this limitation. Further research is needed to gain a deeper understanding of the contributions of the different electronic modalities, the underlying mechanisms, clinical outcomes, and optimal implementation of these devices in clinical practice. Several challenges must be addressed before integrating smart inhalers into daily practice, including technical complexities, limited evidence concerning clinical outcomes, uncertainties about cost-effectiveness, and the issue of funding for the devices [ 18 ]. The TRICOLON study aims to offer additional evidence, potentially bringing us closer to their use in daily practice.

To the best of our knowledge, the TRICOLON trial is the first that aims to investigate whether single inhaler usage in COPD patients receiving triple therapy can improve adherence in a large-scale, randomized, controlled, real-world setting. Moreover, unlike the majority of existing studies focusing on the impact of smart inhalers, the TRICOLON trial distinguishes itself with a prolonged follow-up period of one year. We acknowledge that patients’ adherence may be influenced by their awareness of participating in a study. To minimize this interference, we have limited the number of study visits to closely resemble real-world settings. Additionally, patients are informed that the focus of this study is on the convenience of various treatment options, and adherence is not specifically mentioned in the information provided by the researchers or in the patient information letter. This has been approved by the Medical Ethical Review Board. The Tricolon study not only investigates the impacts of a single inhaler and the use of a smart inhaler on adherence but also evaluates various clinical outcomes, including exacerbation rates, hospitalizations, and disease burden. Nevertheless, the study is powered on the primary outcome adherence to inhalation therapy. Therefore, although not powered for the clinical outcomes or for the correlation between adherence and clinical outcomes, valuable information on these outcomes will be collected to inform possible follow-up studies.

The implementation of an e-health application may present challenges, whether due to technical issues or the potential unfamiliarity among patients and healthcare professionals [ 48 ]. To proactively address these concerns, we dedicated time to thoroughly test the application before the start of the study. This involved multiple stakeholders, including the researchers, the app producer, and patients. Moreover, the application's design is intentionally kept simple and clear, ensuring that individuals of all ages, educational backgrounds, and health literacy levels can easily comprehend and use it. This was confirmed in a previous study where an older, and thus more digitally challenged, population of patients with Idiopathic Pulmonary Fibrosis (IPF) used this app for daily spirometry. The study found that 80% of the participants found the app easy to use, and 90% did not perceive it as burdensome [ 49 ].

Beyond addressing the primary research questions, this TRICOLON study creates an opportunity for a direct comparison between three methods to measure adherence: digital data from the smart inhaler, self-reported data collected through the TAI questionnaire, and drug deposition data in hair. The use of this final technique is relatively uncommon in studies concerning inhalation medication, although it has been used in previous research related to cortisol and in forensic studies [ 22 , 50 ]. In a specific study involving asthma and COPD patients, the measurement of inhalation medication demonstrated a clear dose–response relationship among those using formoterol [ 41 ].

Our identification of a lack of high-quality data on the improvement of adherence of SITT over MITT therapy in COPD and limited data for smart inhalers highlights the need for further research. The multi-centre, randomized controlled, three-arm, real-world TRICOLON trial aims to increase insight in the value of SITT and the added value of electronic adherence monitoring.

Availability of data and materials

All data relevant to the study are included in the article or uploaded as supplementary information. The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

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Acknowledgements

We appreciate the assistance of Carmen van der Heijden, librarian at the Medical Library in the Franciscus Gasthuis & Vlietland hospital, in conducting the PubMed searches. We would like to thank the members of the investigational teams across all participating hospitals for their dedicated time and effort in conducting this study.

TRICOLON study group

The TRICOLON Study Group consortium consists of the individuals listed below:

Liz J.A. Cuperus MD 1,2,3 , Job van der Palen PhD 4 , Arnoud Aldenkamp MD 5 , Astrid van Huisstede MD PhD 6 , Erik W.M.A. Bischoff MD PhD 7 , Job F.M. van Boven PharmD PhD 8 , Folkert Brijker MD 9 , Stephan Dik MD 10 , Jeroen A.J.M. van Excel MD 11 , Martijn Goosens MD 12 , Peter Th.W. van Hal MD PhD 13 , Jolanda C. Kuijvenhoven MD PhD 14 , Lisette I.Z. Kunz MD PhD 15 , Erwin C. Vasbinder PhD 16 , Huib A.M. Kerstjens MD PhD 2 , Johannes C.C.M. in ’t Veen MD PhD 1,3 , Marjo van der Poel 17 , Marijke Amelink 9 , Anke Rol 18 , Jennifer de Graaf 18 , Petra Hirmann 19 , Fleur van Tour 20 , Elly Jordens 13 , Lydia Alfing 13 , Gerda Lenderink 21 , Thecla Rupert 21 , Truus Rietveld 21 , Jasmijn van Campen 15 , Jantine de Bruijn 15 , Janice van ter Burg 15 , Walter van Litsenburg 5 , Len Knoops 22 , Margot Eggermont-Schilt 23 , Manon de Waard-Heijligers 23 , Ilonka Paalvast-Schouten 23 , Sarah van Oord 11

1 Pulmonology Department, Franciscus Gasthuis and Vlietland, Rotterdam, the Netherlands

2 Pulmonology Department, University of Groningen, University Medical Center Groningen, and Groningen Research Institute for Asthma and COPD, Groningen, the Netherlands

3 Pulmonology Department, Erasmus Medical Centre, Rotterdam, the Netherlands

4 Department of Epidemiology, Medisch Spectrum Twente, Enschede, The Netherlands

5 Department of Pulmonary Medicine, Catharina Hospital, Eindhoven, The Netherlands

6 Department of Pulmonology, Northwest Clinics, Alkmaar, the Netherlands

7 Department of Primary and Community Care, Radboud University Medical Center, Nijmegen, Netherlands

8 Department of Clinical Pharmacy & Pharmacology Groningen Research Institute for Asthma and COPD (GRIAC), University Medical Center Groningen, University of Groningen, Groningen, The Netherlands

9 Department of Pulmonary Medicine, Spaarne Gasthuis, Haarlem, The Netherlands

10 Department of Pulmonary Medicine, Albert Schweitzer ziekenhuis, Dordrecht, The Netherlands

11 Department of Pulmonary Medicine, HagaZiekenhuis, The Hague, The Netherlands

12 Department of Pulmonary Medicine, Gelre Ziekenhuizen, Zutphen, The Netherlands

13 Department of Respiratory Medicine, Van Weel-Bethesda Hospital, Dirksland, the Netherlands

14 Department of Respiratory Medicine, Medical Centre Leeuwarden, Leeuwarden, the Netherlands

15 Department of Pulmonology, Haaglanden Medical Centre, The Hague, the Netherlands

16 Department of Clinical Pharmacy, Franciscus Gasthuis, Rotterdam, the Netherlands

17 Spaarne Gasthuis, Haarlem, The Netherlands

18 Northwest Clinics, Alkmaar, the Netherlands

19 Medical Centre Leeuwarden, Leeuwarden, the Netherlands

20 Albert Schweitzer ziekenhuis, Dordrecht, The Netherlands

21 Gelre Ziekenhuizen, Zutphen, The Netherlands

22 Catharina Hospital, Eindhoven, The Netherlands

23 HagaZiekenhuis, The Hague, The Netherlands

The faculty received an unrestricted grant from Chiesi Pharmaceuticals B.V. Furthermore, the funding includes contributions from the research group in the Franciscus Gasthuis & Vlietland hospital and transformation funds from health insurance companies.

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Authors and affiliations.

Pulmonology Department, Franciscus Gasthuis and Vlietland, Rotterdam, the Netherlands

Liz J. A. Cuperus & Johannes C. C. M. in ’t Veen

Pulmonology Department, University of Groningen, University Medical Center Groningen, and Groningen Research Institute for Asthma and COPD, Groningen, the Netherlands

Liz J. A. Cuperus & Huib A. M. Kerstjens

Pulmonology Department, Erasmus Medical Centre, Rotterdam, the Netherlands

Department of Epidemiology, Medisch Spectrum Twente, Enschede, The Netherlands

Job van der Palen

Department of Pulmonary Medicine, Catharina Hospital, Eindhoven, The Netherlands

Arnoud Aldenkamp

Department of Pulmonology, Northwest Clinics, Alkmaar, the Netherlands

Astrid van Huisstede

Department of Primary and Community Care, Radboud University Medical Center, Nijmegen, The Netherlands

Erik W. M. A. Bischoff

Department of Clinical Pharmacy & Pharmacology Groningen Research Institute for Asthma and COPD (GRIAC), University Medical Center Groningen, University of Groningen, Groningen, The Netherlands

Job F. M. van Boven

Department of Pulmonary Medicine, Spaarne Gasthuis, Haarlem, The Netherlands

Folkert Brijker

Department of Pulmonary Medicine, Albert Schweitzer Ziekenhuis, Dordrecht, The Netherlands

Stephan Dik

Department of Pulmonary Medicine, HagaZiekenhuis, The Hague, The Netherlands

Jeroen A. J. M. van Excel

Department of Pulmonary Medicine, Gelre Ziekenhuizen, Zutphen, The Netherlands

Martijn Goosens

Department of Respiratory Medicine, Van Weel-Bethesda Hospital, Dirksland, The Netherlands

Peter Th. W. van Hal

Department of Respiratory Medicine, Medical Centre Leeuwarden, Leeuwarden, The Netherlands

Jolanda C. Kuijvenhoven

Department of Pulmonology, Haaglanden Medical Centre, The Hague, The Netherlands

Lisette I. Z. Kunz

Department of Clinical Pharmacy, Franciscus Gasthuis, Rotterdam, The Netherlands

Erwin C. Vasbinder

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• Liz J. A. Cuperus
• , Job van der Palen
• , Arnoud Aldenkamp
• , Astrid van Huisstede
• , Erik W. M. A. Bischoff
• , Job F. M. van Boven
• , Folkert Brijker
• , Stephan Dik
• , Jeroen A. J. M. van Excel
• , Martijn Goosens
• , Peter Th. W. van Hal
• , Jolanda C. Kuijvenhoven
• , Lisette I. Z. Kunz
• , Erwin C. Vasbinder
• , Huib A. M. Kerstjens
• , Johannes C. C. M. in ’t Veen
• , Marjo van der Poel
• , Marijke Amelink
• , Jennifer de Graaf
• , Petra Hirmann
• , Fleur van Tour
• , Elly Jordens
• , Lydia Alfing
• , Gerda Lenderink
• , Thecla Rupert
• , Truus Rietveld
• , Jasmijn van Campen
• , Jantine de Bruijn
• , Janice ter Burg
• , Walter van Litsenburg
• , Len Knoops
• , Margot Eggermont-Schilt
• , Manon de Waard-Heijligers
• , Ilonka Paalvast-Schouten
•  & Sarah van Oord

Contributions

LC and JV conducted the assessment and selection of articles from the PubMed searches, HK was consulted in case of author disagreements. JV initiated the Tricolon trial and acquired the funding. LC, JV, HK, JvdP, EB, JvB were involved in the study design and protocol. LC is the coordinating investigator, JV is the principal investigator. LC, JV and HK wrote the main manuscript text. All authors have thoroughly read, critically revised, and approved the submitted version of the final manuscript.

Corresponding author

Correspondence to Liz J. A. Cuperus .

Ethics declarations

Ethics approval and consent to participate.

Ethics approval for the Tricolon study was waived by the Medical research Ethics Committees United (NL79938.100.22). This study is performed after approval by the Institutional Research Board and Board of Directors of the participating hospitals. The study is registered at clinicaltrials.gov (NCT05495698). Informed consent was obtained from all subjects.

Consent for publication

Not Applicable.

Competing interests

JvdP: none.

EB: unrestricted grants and speaking fees received from Chiesi Pharmaceuticals B.V., Boehringer Ingelheim bv, GlaxoSmithKline.

JvB: received unrestricted research grants from Aardex, AstraZeneca, Chiesi, European Commission COST Action 19132 (ENABLE), European Respiratory Society CRC “CONNECT”, Novartis, Pfizer, Pill Connect, Trudell Medical and consultancy/speaker fees from AstraZeneca, Chiesi, GSK, Novartis, Teva and Vertex. All payments were unrelated to this manuscript and all paid to his institution (UMCG).

LK: received speaker fees from AZ.

EV: received unrestricted research grants from AstraZeneca and Pfizer.

HK: reports grants and consultancy/advisory board participation from/for AstraZeneca, Boehringer Ingelheim, Chiesi, GlaxoSmithKline, and Novartis, all outside the submitted work. All were paid to his institution.

JiV: received unrestricted faculty research grants from GSK, Teva, AZ, Chiesi, Sanofi, and speaker fees from AZ, GSK, Sanofi, Chiesi, Stichting RoLeX and Health Investment.

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Cuperus, L.J.A., van der Palen, J., Aldenkamp, A. et al. Adherence to single inhaler triple therapy and digital inhalers in Chronic Obstructive Pulmonary Disease: a literature review and protocol for a randomized controlled trial (TRICOLON study). BMC Pulm Med 24 , 317 (2024). https://doi.org/10.1186/s12890-024-03044-3

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Received : 16 February 2024

Accepted : 02 May 2024

Published : 04 July 2024

DOI : https://doi.org/10.1186/s12890-024-03044-3

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Article Contents

Introduction, supplementary material, data availability, acknowledgements.

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Comparative efficacy and safety of bimekizumab in psoriatic arthritis: a systematic literature review and network meta-analysis

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Philip J Mease, Dafna D Gladman, Joseph F Merola, Peter Nash, Stacy Grieve, Victor Laliman-Khara, Damon Willems, Vanessa Taieb, Adam R Prickett, Laura C Coates, Comparative efficacy and safety of bimekizumab in psoriatic arthritis: a systematic literature review and network meta-analysis, Rheumatology , Volume 63, Issue 7, July 2024, Pages 1779–1789, https://doi.org/10.1093/rheumatology/kead705

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To understand the relative efficacy and safety of bimekizumab, a selective inhibitor of IL-17F in addition to IL-17A, vs other biologic and targeted synthetic DMARDs (b/tsDMARDs) for PsA using network meta-analysis (NMA).

A systematic literature review (most recent update conducted on 1 January 2023) identified randomized controlled trials (RCTs) of b/tsDMARDs in PsA. Bayesian NMAs were conducted for efficacy outcomes at Weeks 12–24 for b/tsDMARD-naïve and TNF inhibitor (TNFi)-experienced patients. Safety at Weeks 12–24 was analysed in a mixed population. Odds ratios (ORs) and differences of mean change with the associated 95% credible interval (CrI) were calculated for the best-fitting models, and the surface under the cumulative ranking curve (SUCRA) values were calculated to determine relative rank.

The NMA included 41 RCTs for 22 b/tsDMARDs. For minimal disease activity (MDA), bimekizumab ranked 1st in b/tsDMARD-naïve patients and 2nd in TNFi-experienced patients. In b/tsDMARD-naïve patients, bimekizumab ranked 6th, 5th and 3rd for ACR response ACR20/50/70, respectively. In TNFi-experienced patients, bimekizumab ranked 1st, 2nd and 1st for ACR20/50/70, respectively. For Psoriasis Area and Severity Index 90/100, bimekizumab ranked 2nd and 1st in b/tsDMARD-naïve patients, respectively, and 1st and 2nd in TNFi-experienced patients, respectively. Bimekizumab was comparable to b/tsDMARDs for serious adverse events.

Bimekizumab ranked favourably among b/tsDMARDs for efficacy on joint, skin and MDA outcomes, and showed comparable safety, suggesting it may be a beneficial treatment option for patients with PsA.

For joint efficacy, bimekizumab ranked highly among approved biologic/targeted synthetic DMARDs (b/tsDMARDs).

Bimekizumab provides better skin efficacy (Psoriasis Area and Severity Index, PASI100 and PASI90) than many other available treatments in PsA.

For minimal disease activity, bimekizumab ranked highest of all available b/tsDMARDs in b/tsDMARD-naïve and TNF inhibitor–experienced patients.

PsA is a chronic, systemic, inflammatory disease in which patients experience a high burden of illness [ 1–3 ]. PsA has multiple articular and extra-articular disease manifestations including peripheral arthritis, axial disease, enthesitis, dactylitis, skin psoriasis (PSO) and psoriatic nail disease [ 4 , 5 ]. Patients with PsA can also suffer from related inflammatory conditions, uveitis and IBD [ 4 , 5 ]. Approximately one fifth of all PSO patients, increasing to one quarter of patients with moderate to severe PSO, will develop PsA over time [ 6 , 7 ].

The goal of treatment is to control inflammation and prevent structural damage to minimize disease burden, normalize function and social participation, and maximize the quality of life of patients [ 1 , 4 ]. As PsA is a heterogeneous disease, the choice of treatment is guided by individual patient characteristics, efficacy against the broad spectrum of skin and joint symptoms, and varying contraindications to treatments [ 1 , 4 ]. There are a number of current treatments classed as conventional DMARDs such as MTX, SSZ, LEF; biologic (b) DMARDs such as TNF inhibitors (TNFi), IL inhibitors and cytotoxic T lymphocyte antigen 4 (CTLA4)-immunoglobulin; and targeted synthetic (ts) DMARDs which include phosphodiesterase-4 (PDE4) and Janus kinase (JAK) inhibitors [ 1 , 8 ].

Despite the number of available treatment options, the majority of patients with PsA report that they do not achieve remission and additional therapeutic options are needed [ 9 , 10 ]. Thus, the treatment landscape for PsA continues to evolve and treatment decisions increase in complexity, especially as direct comparative data are limited [ 2 ].

Bimekizumab is a monoclonal IgG1 antibody that selectively inhibits IL-17F in addition to IL-17A, which is approved for the treatment of adults with active PsA in Europe [ 11 , 12 ]. Both IL-17A and IL-17F are pro-inflammatory cytokines implicated in PsA [ 11 , 13 ]. IL-17F is structurally similar to IL-17A and expressed by the same immune cells; however, the mechanisms that regulate expression and kinetics differ [ 13 , 14 ]. IL-17A and IL-17F are expressed as homodimers and as IL-17A–IL-17F heterodimers that bind to and signal via the same IL-17 receptor A/C complex [ 13 , 15 ].

In vitro studies have demonstrated that the dual inhibition of both IL-17A and IL-17F with bimekizumab was more effective at suppressing PsA inflammatory genes and T cell and neutrophil migration, and periosteal new bone formation, than blocking IL-17A alone [ 11 , 14 , 16 , 17 ]. Furthermore, IL-17A and IL-17F protein levels are elevated in psoriatic lesions and the superiority of bimekizumab 320 mg every 4 weeks (Q4W) or every 8 weeks (Q8W) over the IL-17A inhibitor, secukinumab, in complete clearance of psoriatic skin was demonstrated in a head-to-head trial in PSO [ 16 , 18 ]. Collectively, this evidence suggests that neutralizing both IL-17F and IL-17A may provide more potent abrogation of IL-17-mediated inflammation than IL-17A alone.

Bimekizumab 160 mg Q4W demonstrated significant improvements in efficacy outcomes compared with placebo, and an acceptable safety profile in adults with PsA in the phase 3 RCTs BE OPTIMAL (NCT03895203) (b/tsDMARD-naïve patients) and BE COMPLETE (NCT03896581) (TNFi inadequate responders) [ 19 , 20 ].

The objective of this study was to establish the comparative efficacy and safety of bimekizumab 160 mg Q4W vs other available PsA treatments, using network meta-analysis (NMA).

Search strategy

A systematic literature review (SLR) was conducted according to the Preferred Reporting Items for Systematic Reviews (PRISMA) guidelines [ 21 ] and adhered to the principles outlined in the Cochrane Handbook for Systematic Reviews of Interventions, Centre for Reviews and Dissemination’s Guidance for Undertaking Reviews in Healthcare, and Methods for the Development of National Institute of Health and Care Excellence (NICE) Public Health Guidance [ 22–24 ]. The SLR of English-language publications was originally conducted on 3 December 2015, with updates on 7 January 2020, 2 May 2022 and 1 January 2023 in Medical Literature Analysis and Retrieval System Online (MEDLINE ® ), Excerpta Medica Database (Embase ® ) and the Cochrane Central Register of Controlled Trials (CENTRAL) for literature published from January 1991 onward using the Ovid platform. Additionally, bibliographies of SLRs and meta-analyses identified through database searches were reviewed to ensure any publications not identified in the initial search were included in this SLR. Key clinical conference proceedings not indexed in Ovid (from October 2019 to current) and ClinicalTrials.gov were also manually searched. The search strategy is presented in Supplementary Table S1 (available at Rheumatology online).

Study inclusion

Identified records were screened independently and in duplicate by two reviewers and any discrepancies were reconciled via discussion or a third reviewer. The SLR inclusion criteria were defined by the Patient populations, Interventions, Comparators, Outcome measures, and Study designs (PICOS) Statement ( Supplementary Table S2 , available at Rheumatology online). The SLR included published studies assessing approved therapies for the treatment of PsA. Collected data included study and patient population characteristics, interventions, comparators, and reported clinical and patient-reported outcomes relevant to PsA. For efficacy outcomes, pre-crossover data were extracted in studies where crossover occurred. All publications included in the analysis were evaluated according to the Cochrane risk-of-bias tool for randomized trials as described in the Cochrane Handbook [ 25 ].

Network meta-analysis methods

NMA is the quantitative assessment of relative treatment effects and associated uncertainty of two or more interventions [ 26 , 27 ]. It is used frequently in health technology assessment, guideline development and to inform treatment decision making in clinical practice [ 26 ].

Bimekizumab 160 mg Q4W was compared with current b/tsDMARDs at regulatory-approved doses ( Table 1 ) by NMA. All comparators were selected on the basis they were relevant to clinical practice, i.e. recommended by key clinical guidelines, licensed by key regulatory bodies and/or routinely used.

NMA intervention and comparators

See Supplementary Table S4 , available at Rheumatology online for additional dosing schedules used in included studies. BID: twice daily; CTLA4-Ig: cytotoxic T lymphocyte antigen 4-immunoglobulin; IL-17A/17Fi: IL-17A/17F inhibitor; IL-17Ai: IL-17A inhibitor; IL-12/23i: IL-12/23 inhibitor; IL-23i: IL-23 inhibitor; JAKi: Janus kinase inhibitor; NMA: network meta-analysis; PDE-4i: phosphodiesterase-4 inhibitor; Q1W: once weekly; Q2W: every 2 weeks; Q4W: every 4 weeks; Q8W: every 8 weeks; Q12W: every 12 weeks; QD: once daily; TNFi: TNF inhibitor.

Two sets of primary analyses were conducted, one for a b/tsDMARD-naïve PsA population and one for a TNFi-experienced PsA population. Prior treatment with TNFis has been shown to impact the response to subsequent bDMARD treatments [ 28 ]. In addition, most trials involving b/tsDMARDs for the treatment of PsA (including bimekizumab) report separate data on both b/tsDMARD-naïve and TNFi-experienced subgroups, making NMA in each of these patient populations feasible.

For each population the following outcomes were analysed: American College of Rheumatology response (ACR20/50/70), Psoriasis Area and Severity Index (PASI90/100), and minimal disease activity (MDA). The analysis of serious adverse events (SAE) was conducted using a mixed population (i.e. b/tsDMARD-naïve, TNFi-experienced and mixed population data all were included) as patients’ previous TNFI exposure was not anticipated to impact safety outcomes following discussions with clinicians. The NMA included studies for which data were available at week 16, if 16-week data were not available (or earlier crossover occurred), data available at weeks 12, 14 or 24 were included. Pre-crossover data were included in the analyses for efficacy outcomes to avoid intercurrent events.

Heterogeneity between studies for age, sex, ethnicity, mean time since diagnosis, concomitant MTX, NSAIDs or steroid use was assessed using Grubb’s test, also called the extreme Studentized deviate method, to identify outlier studies.

All univariate analyses involved a 10 000 run-in iteration phase and a 10 000-iteration phase for parameter estimation. All calculations were performed using the R2JAGS package to run Just Another Gibbs Sampler (JAGS) 3.2.3 and the code reported in NICE Decision Support Unit (DSU) Technical Support Document Series [ 29–33 ]. Convergence was confirmed through inspection of the ratios of Monte-Carlo error to the standard deviations of the posteriors; values >5% are strong signs of convergence issues [ 31 ]. In some cases, trials reported outcome results of zero (ACR70, PASI100, SAE) in one or more arms for which a continuity correction was applied to mitigate the issue, as without the correction most models were not convergent or provided a large posterior distribution making little clinical sense [ 31 ].

Four NMA models [fixed effects (FE) unadjusted, FE baseline risk-adjusted, random effects (RE) unadjusted and RE baseline risk-adjusted] were assessed and the best-fit models were chosen using methods described in NICE DSU Technical Support Document 2 [ 31 ]. Odds ratios (ORs) and differences of mean change (MC) with the associated 95% credible intervals (CrIs) were calculated for each treatment comparison in the evidence network for the best fitting models and presented in league tables and forest plots. In addition, the probability of bimekizumab 160 mg Q4W being better than other treatments was calculated using surface under the cumulative ranking curve (SUCRA) to determine relative rank. Conclusions (i.e. better/worse or comparable) for bimekizumab 160 mg Q4W vs comparators were based on whether the pairwise 95% CrIs of the ORs/difference of MC include 1 (dichotomous outcomes), 0 (continuous outcomes) or not. In the case where the 95% CrI included 1 or 0, then bimekizumab 160 mg Q4W and the comparator were considered comparable. If the 95% CrI did not include 1 or 0, then bimekizumab 160 mg Q4W was considered either better or worse depending on the direction of the effect.

Compliance with ethics guidelines

This article is based on previously conducted studies and does not contain any new studies with human participants or animals performed by any of the authors.

Study and patient characteristics

The SLR identified 4576 records through databases and 214 records through grey literature, of which 3143 were included for abstract review. Following the exclusion of a further 1609 records, a total of 1534 records were selected for full-text review. A total of 66 primary studies from 246 records were selected for data extraction. No trial was identified as having a moderate or high risk of bias ( Supplementary Table S3 , available at Rheumatology online).

Of the 66 studies identified in the SLR, 41 studies reported outcomes at weeks 12, 16 or 24 and met the criteria for inclusion in the NMA in either a b/tsDMARD-naïve population ( n  = 20), a TNFi-experienced population ( n  = 5), a mixed population with subgroups ( n  = 13) or a mixed PsA population without subgroups reported ( n  = 3). The PRISMA diagram is presented in Fig. 1 . Included and excluded studies are presented in Supplementary Tables S4 and S5 , respectively (available at Rheumatology online).

PRISMA flow diagram. The PRISMA flow diagram for the SLR conducted to identify published studies assessing approved treatments for the treatment of PsA. cDMARD: conventional DMARD; NMA: network meta-analysis; NR: not reported; PD: pharmacodynamic; PK: pharmacokinetic; PRISMA: Preferred Reporting Items for Systematic Reviews and Meta-Analyses; RCT: randomized controlled trial; SLR: systematic literature review

The baseline study and patient characteristics (where reported) are presented in Supplementary Table S6 (available at Rheumatology online). There were 20–483 patients included in treatment arms. The median age of patients was 48.9 years, the median percentage of males was 50.3% and a median of 92.3% of patients were Caucasian. Patients had a mean time since diagnosis of 7.6 years and a mean PASI score of 8.7. The mean (range) use of concomitant MTX, NSAIDs and steroids were 53.9% (29.1% to 84.0%), 72.4% (33.3% to 100.0%) and 16.8% (9.2% to 30.0%), respectively. Heterogeneity was generally low across studies except for the concomitant use of MTX, NSAIDs and steroids. Using an approach consistent with established NMA methods in PsA [ 34–36 ], a meta-regression model using JAGS code reported in NICE DSU Technical Support Document 3 [ 33 ] was used to account for variation in placebo responses when model-fit statistics suggested that baseline risk-adjusted models provided a better fit to the data.

NMA results

The network diagrams for ACR50 in b/tsDMARD-naïve and TNFi-experienced patients are presented in Fig. 2A and B with network diagrams for other outcomes presented in Supplementary Fig. S1 (available at Rheumatology online). The networks for ACR response were larger, in terms of both number of studies and patients included, than the networks for PASI. Similarly, the networks for b/tsDMARD-naïve patients were larger than TNFi-experienced patients across all outcomes analysed. Placebo was used as a common comparator in all networks and there were a few studies that included more than two arms (OPAL-Broaden, Select-PsA-1, SPIRIT-P1 and BE OPTIMAL) that included adalimumab as the reference arm in b/tsDMARD-naïve patients. Lastly, networks included studies where the primary outcome was evaluated at time points longer than 16 weeks (e.g. EXCEED study at 52 weeks) but as per the methods, 16-week data formed the network.

Network of evidence for ACR50. ( A ) b/tsDMARD-naïve patients. ( B ) TNFi-experienced patients. The size of the circle representing each intervention is proportional to the number of patients included in the analysis. The line width is proportional to the number of studies connecting the interventions. ABA: abatacept; ADA: adalimumab; APR: apremilast; b/tsDMARD-naïve: biologic and targeted synthetic DMARD-naïve; BKZ: bimekizumab; CZP: certolizumab pegol; ETA: etanercept; GOL: golimumab; GUS: guselkumab; IFX: infliximab; IV: intravenous; IXE: ixekizumab; PBO: placebo; Q4W: every 4 weeks; Q8W: every 8 weeks; RIS: risankizumab; SEC: secukinumab; TNFi-experienced: TNF inhibitor–experienced; TOF: tofacitinib; UPA: upadacitinib; UST: ustekinumab; w/o LD: without loading dose

The best-fit model is noted for each outcome with full model fit statistics for all outcomes presented in Supplementary Table S7 (available at Rheumatology online). Forest plots for ACR50 and PASI100 are presented in Figs 3 and 4 , with forest plots for other outcomes, along with the league tables in Supplementary Fig. S2 and Table S8 , respectively (available at Rheumatology online).

ACR50. The results for the NMA on ACR50 at week 16. ( A ) b/tsDMARD-naïve patients including forest plot and SUCRA values. FE baseline–adjusted model DIC = 469.59. ( B ) TNFi-experienced patients including forest plot and SUCRA values. RE-unadjusted model DIC = 205.33. a Week 24 data were used as week 16 data was not available. * The 95% CrI does not include 1; bimekizumab 160 mg Q4W is considered either better or worse depending on the direction of the effect. ABA: abatacept; ADA: adalimumab; APR: apremilast; b/tsDMARD-naïve: biologic and targeted synthetic DMARD-naïve; BKZ: bimekizumab; CrI: credible interval; CZP: certolizumab pegol; DIC: deviance information criterion; ETA: etanercept; FE: fixed effects; GOL: golimumab; GUS: guselkumab; IFX: infliximab; IV: intravenous; IXE: ixekizumab; NMA: network meta-analysis; PBO: placebo; Q4W: every 4 weeks; Q8W: every 8 weeks; RE: random effects; RIS: risankizumab; SEC: secukinumab; SUCRA: surface under the cumulative ranking curve; TNFi-experienced: TNF inhibitor–experienced; TOF: tofacitinib; UPA: upadacitinib; UST: ustekinumab; w/o LD: without loading dose

PASI100. The results for the NMA on PASI100 at week 16: ( A ) b/tsDMARD-naïve patients including forest plot and SUCRA values. FE baseline–adjusted model DIC = 150.27. ( B ) TNFi-experienced patients including forest plot and SUCRA values. RE-unadjusted model DIC = 81.76. a Week 24 data were used as week 16 data was not available. * The 95% CrI does not include 1; bimekizumab 160 mg 4W is considered better. ADA: adalimumab; b/tsDMARD-naïve: biologic and targeted synthetic DMARD-naïve; BKZ, bimekizumab; CrI, credible interval; CZP, certolizumab pegol; DIC, deviance information criterion; FE, fixed effects; GOL, golimumab; GUS, guselkumab; IXE, ixekizumab; NMA, network meta-analysis; PASI, Psoriasis Area and Severity Index; PBO, placebo; Q4W, every 4 weeks; Q8W, every 8 weeks; RE, random effects; SEC, secukinumab; SUCRA, surface under the cumulative ranking curve; TNFi-experienced, TNF inhibitor–experienced; UPA, upadacitinib

Joint outcomes

For ACR50 outcomes, the best-fit models for b/tsDMARD-naïve and TNFi-experienced were the FE baseline–adjusted model and RE-unadjusted model, respectively.

b/tsDMARD-naïve patients

Bimekizumab 160 mg Q4W ranked 6th for ACR20 (SUCRA = 0.75), 5th for ACR50 (SUCRA = 0.74) ( Fig. 3A ) and 3rd for ACR70 (SUCRA = 0.80) among 21 treatments. For ACR50, bimekizumab 160 mg Q4W was better than placebo, abatacept 125 mg, guselkumab 100 mg Q4W, ustekinumab 45 mg, risankizumab 150 mg, guselkumab 100 mg Q8W and ustekinumab 90 mg; worse than golimumab 2 mg i.v.; and comparable to the remaining treatments in the network ( Fig. 3A ).

TNFi-experienced patients

Bimekizumab 160 mg Q4W ranked 1st among 16 treatments for ACR20 (SUCRA = 0.96), 2nd among 15 treatments for ACR50 (SUCRA = 0.84) ( Fig. 3B ) and 1st among 16 treatments for ACR70 (SUCRA = 0.83). Bimekizumab 160 mg Q4W was better than placebo, abatacept 125 mg, secukinumab 150 mg without loading dose, tofacitinib 5 mg and secukinumab 150 mg; and comparable to the remaining treatments in the network on ACR50 ( Fig. 3B ).

Skin outcomes

For PASI100 outcomes, the best-fit models for b/tsDMARD-naïve and TNFi-experienced were the FE baseline–adjusted model and RE-unadjusted model, respectively.

Bimekizumab 160 mg Q4W ranked 2nd among 15 treatments (SUCRA = 0.89) for PASI90 and 1st among 11 treatments (SUCRA = 0.95) for PASI100 ( Fig. 4A ). Bimekizumab 160 mg Q4W was better than placebo, certolizumab pegol pooled, golimumab 2 mg i.v., secukinumab 150 mg, adalimumab 40 mg, upadacitinib 15 mg, secukinumab 300 mg and ixekizumab 80 mg Q4W; and comparable to the remaining treatments in the network on PASI100 ( Fig. 4A ).

Bimekizumab 160 mg Q4W ranked 1st among 10 treatments (SUCRA = 0.85) for PASI90 and 2nd among 7 treatments (SUCRA = 0.79) for PASI100 ( Fig. 4B ). Bimekizumab 160 mg Q4W was better than placebo, ixekizumab 80 mg Q4W and upadacitinib 15 mg; and comparable to the remaining treatments in the network on PASI100 ( Fig. 4B ).

For MDA, the best-fit models for b/tsDMARD-naïve and TNFi-experienced were the FE baseline–adjusted model and RE-unadjusted model, respectively.

Bimekizumab 160 mg Q4W ranked 1st among 13 treatments (SUCRA = 0.91) and was better than placebo [OR (95% CrI) 6.31 (4.61–8.20)], guselkumab 100 mg Q4W [2.06 (1.29–3.10)], guselkumab 100 mg Q8W [1.76 (1.09–2.69)], risankizumab 150 mg [1.99 (1.40–2.76)] and adalimumab 40 mg [1.41 (1.01–1.93)]; and comparable to the remaining treatments in the network ( Supplementary Fig. S2G , available at Rheumatology online).

Bimekizumab 160 mg Q4W ranked 1st among 11 treatments (SUCRA = 0.83) and was better than placebo [12.10 (5.31–28.19)] and tofacitinib 5 mg [6.81 (2.14–21.35)]; and comparable to the remaining treatments in the network ( Supplementary Fig. S2H , available at Rheumatology online).

The network for SAEs for a mixed population included 23 treatments and the best-fit model was an RE-unadjusted model (due to study populations and time point reporting heterogeneity). Bimekizumab 160 mg Q4W showed comparable safety to all treatments in the network ( Supplementary Fig. S2I , available at Rheumatology online).

The treatment landscape for PsA is complex, with numerous treatment options and limited direct comparative evidence. Bimekizumab 160 mg Q4W has recently been approved for the treatment of active PsA by the European Medicines Agency and recommended by NICE in the UK, and the published phase 3 results warrant comparison with existing therapies by NMA.

This NMA included 41 studies evaluating 22 b/tsDMARDs including the novel IL-17F and IL-17A inhibitor, bimekizumab. Overall, bimekizumab 160 mg Q4W ranked favourably among b/tsDMARDS for efficacy in joint, skin and disease activity outcomes in PsA across both b/tsDMARD-naïve and TNFi-experienced populations. The safety of bimekizumab 160 mg Q4W was similar to the other b/tsDMARDs.

The Group for Research and Assessment of Psoriasis and Psoriatic Arthritis (GRAPPA) and EULAR provide evidence-based recommendations for the treatment of PsA [ 1 , 2 ]. To treat peripheral arthritis symptoms in PsA, efficacy across the classes of current b/tsDMARDs are considered similar by both GRAPPA and EULAR, in part due to a lack of data comparing licensed therapies in a head-to-head trial setting [ 1 , 2 ]. EULAR recommends the use of JAK inhibitors in the case of inadequate response, intolerance or when a bDMARD is not appropriate [ 1 ]. This recommendation was made when tofacitinib was the only available JAK inhibitor, but reflects current marketing authorizations for tofacitinib and upadacitinib which indicate use in patients with an inadequate response or prior intolerance to TNFis (USA) or bDMARDs (Europe) [ 37–40 ]. This NMA suggests that bimekizumab 160 mg Q4W may have an advantage over current treatments, including IL-23 inhibitors in b/tsDMARD naïve patients, and secukinumab 150 mg and tofacitinib in TNFi-experienced patients, as evidenced by our analysis of ACR50 for which the pairwise comparisons were significantly in favour of bimekizumab 160 mg Q4W.

For the treatment of skin symptoms in PsA, IL-23, IL-12/23 and IL-17A inhibitors are currently recommended due to their greater efficacy compared with TNFis [ 1 , 4 ]. GRAPPA also suggests considering efficacy demonstrated in direct comparative studies in PSO when selecting a treatment for PsA skin symptoms [ 2 ]. In our analysis of complete skin clearance as measured by PASI100, bimekizumab 160 mg Q4W demonstrated the likelihood of significantly greater efficacy than IL-17A, JAK inhibitors and TNFis in b/tsDMARD-naïve patients and IL-17A and JAK inhibitors in TNFi-experienced patients. Furthermore, the NMA results for skin clearance in PsA are in alignment with previous studies in PSO that demonstrated superiority of bimekizumab 320 mg Q4W or Q8W vs secukinumab, ustekinumab and adalimumab ( P  < 0.001) (note that the dosing of bimekizumab in PSO differs from that in PsA) [ 12 , 18 , 41 , 42 ].

There are similarities between our results and other recently published NMAs of b/tsDMARDs in PsA, although methodological heterogeneity across all NMAs makes comparisons challenging [ 34–36 , 43–45 ]. Among recent NMAs, the largest evaluated 21 treatments [ 34 ] and only four considered subgroups of b/tsDMARD-naïve and TNFi-experienced patients or those with inadequate response [ 35 , 36 , 43 , 45 ]. Furthermore, different or pooled levels of response were evaluated for ACR and PASI outcomes.

Previous NMAs also support IL-17, IL-12/23 and IL-23 inhibitors having greater efficacy for skin symptoms than TNFis [ 35 , 36 ]. In an overall PsA population, McInnes et al. demonstrated that secukinumab 300 mg, ixekizumab 80 mg Q4W, and ustekinumab 45 mg and 90 mg were likely more efficacious than TNFis for PASI90 [ 35 ]. In another NMA by Ruyssen-Witrand et al. , results suggested that ixekizumab 80 mg Q4W had significantly greater efficacy than adalimumab, certolizumab pegol pooled, and etanercept 25 mg twice weekly/50 mg once weekly for any PASI score (50%, 75%, 90% and 100% reduction) in bDMARD-naïve patients [ 36 ].

For joint outcomes, Mease et al. compared guselkumab Q4W and Q8W with other b/tsDMARDs in a network of 21 treatments in an overall PsA population for ACR50 [ 34 ]. Both guselkumab dosing schedules were better than abatacept and apremilast, but golimumab 2 mg i.v. had a higher likelihood of ACR50 response than guselkumab Q8W [ 34 ]. Despite MDA being assessed in clinical trials for bDMARD therapies and a treatment target in PsA [ 46 ], evidence for comparative efficacy for this outcome is limited. None of the most recent NMAs before this one included an analysis of MDA [ 34–36 ]. With regard to safety outcomes, previous NMAs evaluating SAEs also resulted in either no difference between b/tsDMARDs vs placebo or other b/tsDMARDs [ 34 , 36 , 44 , 45 ].

This study has a number of strengths. To our knowledge this NMA represents the most comprehensive and in-depth comparative efficacy analysis of approved treatments in PsA to date. The evidence was derived from a recent SLR, ensuring that new RCTs and updated results from previously published RCTs were included. It is also the first NMA to include the phase 3 BE COMPLETE and BE OPTIMAL trials of bimekizumab [ 19 , 20 ]. Our NMA used robust methods and accounted for variation in placebo response through network meta-regression in accordance with NICE DSU Technical Support Documents [ 31–33 ]. As an acknowledgement of the evolution of treatment advances, separate analyses of b/tsDMARD-naïve and TNFi-experienced subgroups were conducted with the intent to assist healthcare decision-making in different clinical settings. In addition, a panel of clinical experts were consulted from project inception and are authors of this paper, ensuring inclusion of a comprehensive set of clinically meaningful outcomes, including the composite, treat-to-target outcome of MDA.

Despite the robust evidence base and methodology, this NMA has limitations. Indirect treatment comparisons such as this NMA are not a substitute for head-to-head trials. There was heterogeneity in the endpoints and reporting in the included studies. Fewer studies reporting PASI outcomes resulted in smaller networks compared with the network of studies evaluating ACR response criteria. Not all trials reported outcomes at the same timepoint, thereby reducing the comparability of trial results, which has been transparently addressed by noting where week 24 data were used vs week 12, 14 or 16 data. The analyses for the TNFi-experienced population were limited by potential heterogeneity, especially in the analyses where fewer studies were included in the networks, as this group could include patients who had an inadequate response to TNFi or discontinued TNFi treatment due to other reasons (e.g. lost access). Also, in the analyses for the TNFi-experienced population, very low patient numbers for some treatments resulted in less statistical power. Additionally, the data included in the analysis were derived exclusively from RCTs, for which the study populations may not reflect a typical patient population seen in real-world practice. For example, trial results may be different in patients with oligoarthritis who are not well-represented in clinical trials.

Over the years covering our SLR, we acknowledge that patient populations and the PsA treatment landscape have evolved. After a thorough review of baseline patient characteristics, no significant differences were observed across the studies included in the NMA. To further mitigate uncertainty, baseline regression was used to actively correct for changes in the placebo rate over time ensuring a consistent and fair comparison across all included treatments. In addition, our analyses were conducted in separate b/tsDMARD-naïve and TNFi-experienced populations that reflect the evolving PsA patient population over time. Radiographic progression was not within the purview of this NMA because the NMA focused on a shorter timeframe than the 52-week duration typically recommended by the literature for investigating radiographic progression. Furthermore, there is existing literature on this topic, as exemplified by the work of Wang et al. in 2022 [ 47 ]. Nevertheless, the comprehensive and current evidence base, examination of multiple endpoints, and consistency with previous reported NMAs lend credence to our results.

Overall, the results of this NMA demonstrated the favourable relative efficacy and safety of bimekizumab 160 mg Q4W vs all approved treatments for PsA. Bimekizumab ranked high in terms of efficacy on joint, skin and MDA outcomes in both b/tsDMARD-naïve and TNFi-experienced patient populations, and showed comparable safety to other treatments. In the evolving PsA treatment landscape, bimekizumab 160 mg Q4W is a potentially beneficial treatment option for patients with PsA.

Supplementary material is available at Rheumatology online.

The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request.

This study was funded in full by UCB Pharma.

Disclosure statement : P.J.M.: has received research grants from AbbVie, Amgen, BMS, Eli Lilly, Gilead, Janssen, Novartis, Pfizer, Sun Pharma and UCB Pharma; consultancy fees from AbbVie, Acelyrin, Aclaris, Amgen, BMS, Boehringer Ingelheim, Eli Lilly, Galapagos, Gilead, GSK, Janssen, Moonlake Pharma, Novartis, Pfizer, Sun Pharma and UCB Pharma; and speakers’ bureau for AbbVie, Amgen, Eli Lilly, Janssen, Novartis, Pfizer and UCB Pharma. L.C.C.: received grants/research support from AbbVie, Amgen, Celgene, Eli Lilly, Janssen, Novartis, Pfizer and UCB; worked as a paid consultant for AbbVie, Amgen, Bristol Myers Squibb, Celgene, Eli Lilly, Gilead, Galapagos, Janssen, Moonlake, Novartis, Pfizer and UCB; and has been paid as a speaker for AbbVie, Amgen, Biogen, Celgene, Eli Lilly, Galapagos, Gilead, GSK, Janssen, Medac, Novartis, Pfizer and UCB. D.D.G.: consultant and/or received grant support from Abbvie, Amgen, BMS, Celgene, Eli Lilly, Galapagos, Gilead, Janssen, Novartis, Pfizer and UCB. J.F.M.: consultant and/or investigator for AbbVie, Amgen, Biogen, BMS, Dermavant, Eli Lilly, Janssen, LEO Pharma, Novartis, Pfizer, Regeneron, Sanofi, Sun Pharma and UCB Pharma. P.N.: research grants, clinical trials and honoraria for advice and lectures on behalf of AbbVie, Boehringer Ingelheim, BMS, Eli Lilly, Galapagos/Gilead, GSK, Janssen, Novartis, Pfizer, Samsung, Sanofi and UCB Pharma. S.G. and V.L.-K.: employees of Cytel, Inc. which served as a consultant on the project. A.R.P., D.W. and V.T.: employees and stockholders of UCB Pharma.

The authors acknowledge Leah Wiltshire of Cytel for medical writing and editorial assistance based on the authors’ input and direction, Heather Edens (UCB Pharma, Smyrna, GA, USA) for publication coordination and Costello Medical for review management, which were funded by UCB Pharma. This analysis was funded by UCB Pharma in accordance with Good Publication Practice (GPP 2022) guidelines ( http://www.ismpp.org/gpp-2022 ). Data were previously presented at ISPOR-US 2023 (Boston, MA, USA, 7–10 May 2023).

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