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Smart education: a review and future research directions  †.

1. Introduction

2. literature review, 2.1. search methodology, 2.2. search results, 3. developed systems, 4. research opportunities.

• Connectivity . Several Smart Education systems tested the speed of their communications and discovered that there is a great reduction in performance as more devices connect. This entails a problem since the trend is having more and more students per classroom. A possible improvement could be to create a specific a protocol for mixed communications (AR and VR with RFID or other sensors). A protocol like that could respond more quickly and/or introduce more elements into the systems.
• Security . The collection of personal data of students, teachers or even management personnel are very common in Smart Education environments. More research is therefore needed regarding the ethical aspects of data collection, including privacy and secure data management, among others.
• Prediction systems . Another relevant research line to be developed is the prediction of events before they occur, such as students dropping out or failing a course. In this way, it would be possible to take corrective measures and/or increase resources, resources with the aim to improve teachers an students’ performance.
• Data visualization . Although several papers already focus on data visualization techniques and dashboards, there is still a long way to go to deal with the large amount of data generated in Smart Education environments, display them correctly and make this data easier to understand for students and teachers. This research topic is important in order to combine existing administrative data with data collected from Smart Education environments.

5. Conclusions

Acknowledgments.

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Share and Cite

Martín, A.C.; Alario-Hoyos, C.; Kloos, C.D. Smart Education: A Review and Future Research Directions. Proceedings 2019 , 31 , 57. https://doi.org/10.3390/proceedings2019031057

Martín AC, Alario-Hoyos C, Kloos CD. Smart Education: A Review and Future Research Directions. Proceedings . 2019; 31(1):57. https://doi.org/10.3390/proceedings2019031057

Martín, Adrián Carruana, Carlos Alario-Hoyos, and Carlos Delgado Kloos. 2019. "Smart Education: A Review and Future Research Directions" Proceedings 31, no. 1: 57. https://doi.org/10.3390/proceedings2019031057

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The future of research: Emerging trends and new directions in scientific inquiry

The world of research is constantly evolving, and staying on top of emerging trends is crucial for advancing scientific inquiry. With the rapid development of technology and the increasing focus on interdisciplinary research, the future of research is filled with exciting opportunities and new directions.

In this article, we will explore the future of research, including emerging trends and new directions in scientific inquiry. We will examine the impact of technological advancements, interdisciplinary research, and other factors that are shaping the future of research.

One of the most significant trends shaping the future of research is the rapid development of technology. From big data analytics to machine learning and artificial intelligence, technology is changing the way we conduct research and opening up new avenues for scientific inquiry. With the ability to process vast amounts of data in real-time, researchers can gain insights into complex problems that were once impossible to solve.

Another important trend in the future of research is the increasing focus on interdisciplinary research. As the boundaries between different fields of study become more fluid, interdisciplinary research is becoming essential for addressing complex problems that require diverse perspectives and expertise. By combining the insights and methods of different fields, researchers can generate new insights and solutions that would not be possible with a single-discipline approach.

One emerging trend in research is the use of virtual and augmented reality (VR/AR) to enhance scientific inquiry. VR/AR technologies have the potential to transform the way we conduct experiments, visualize data, and collaborate with other researchers. For example, VR/AR simulations can allow researchers to explore complex data sets in three dimensions, enabling them to identify patterns and relationships that would be difficult to discern in two-dimensional representations.

Another emerging trend in research is the use of open science practices. Open science involves making research data, methods, and findings freely available to the public, facilitating collaboration and transparency in the scientific community. Open science practices can help to accelerate the pace of research by enabling researchers to build on each other’s work more easily and reducing the potential for duplication of effort.

The future of research is also marked by scientific innovation, with new technologies and approaches being developed to address some of the world’s most pressing problems. For example, gene editing technologies like CRISPR-Cas9 have the potential to revolutionize medicine by allowing scientists to edit DNA and cure genetic diseases. Similarly, nanotechnology has the potential to create new materials with unprecedented properties, leading to advances in fields like energy, electronics, and medicine.

One new direction in research is the focus on sustainability and the environment. With climate change and other environmental issues becoming increasingly urgent, researchers are turning their attention to developing sustainable solutions to the world’s problems. This includes everything from developing new materials and technologies to reduce greenhouse gas emissions to developing sustainable agricultural practices that can feed the world’s growing population without damaging the environment.

Another new direction in research is the focus on mental health and wellbeing. With mental health issues becoming increasingly prevalent, researchers are exploring new approaches to understanding and treating mental illness. This includes everything from developing new therapies and medications to exploring the role of lifestyle factors like diet, exercise, and sleep in mental health.

In conclusion, the future of research is filled with exciting opportunities and new directions. By staying on top of emerging trends, embracing interdisciplinary research, and harnessing the power of technological innovation, researchers can make significant contributions to scientific inquiry and address some of the world’s most pressing problems.

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Please note you do not have access to teaching notes, timeline of engagement research and future research directions.

Management Research Review

ISSN : 2040-8269

Article publication date: 28 March 2018

Issue publication date: 9 April 2018

Studies suggest that engagement is related with organizationally desired outcomes, including performance, productivity, profitability, employee retention, organization citizenship behavior and employee well-being. Despite its practical relevance in the workplace, the concept of engagement has been theoretically dispersed. Therefore, this study aims to present a conceptual review of engagement studies leading to the development of a nomological framework and an evolution timeline for the concept.

Design/methodology/approach

The present study is divided into three sections. The first section elicits the nomological framework based on the comparison between engagement, its predecessors and its contemporary concepts such as motivation theories, job design theories, burnout theories and positive psychology. A review of related theories and concepts highlights the similarities and differences vis-a-vis engagement. In the second section, the study depicts the evolution of the engagement concept based on the nomological framework. The evolution is discussed through the decades of before 1990, 1990-2000, 2000-2010 and 2010 onwards. To consolidate the theories and concepts, the authors covered studies that defined engagement as role engagement, personal engagement, work engagement and employee engagement. The third section presents the future research directions based on the framework and evolution.

The literature review reveals future research directions. These include the addition of new antecedents and theoretical frameworks to enrich the explanatory power and practical relevance of the antecedents of engagement, exploring the context of work with qualitative and mixed method designs, exploring the unit of “role” in engagement studies and the need for more replication studies in this field.

Originality/value

The key contributions of this paper are the nomological framework and the timeline of the evolution of engagement concept.

• Positive psychology
• Organizational theory and behaviour
• Evolution timeline
• Nomological framework

Kunte, M. and Rungruang, P. (2018), "Timeline of engagement research and future research directions", Management Research Review , Vol. 41 No. 4, pp. 433-452. https://doi.org/10.1108/MRR-04-2017-0123

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Home » Future Research – Thesis Guide

Future Research – Thesis Guide

Table of Contents

Future Research

Definition:

Future research refers to investigations and studies that are yet to be conducted, and are aimed at expanding our understanding of a particular subject or area of interest. Future research is typically based on the current state of knowledge and seeks to address unanswered questions, gaps in knowledge, and new areas of inquiry.

How to Write Future Research in Thesis

Here are some steps to help you write effectively about future research in your thesis :

• Identify a research gap: Before you start writing about future research, identify the areas that need further investigation. Look for research gaps and inconsistencies in the literature , and note them down.
• Specify research questions : Once you have identified a research gap, create a list of research questions that you would like to explore in future research. These research questions should be specific, measurable, and relevant to your thesis.
• Discuss limitations: Be sure to discuss any limitations of your research that may require further exploration. This will help to highlight the need for future research and provide a basis for further investigation.
• Suggest methodologies: Provide suggestions for methodologies that could be used to explore the research questions you have identified. Discuss the pros and cons of each methodology and how they would be suitable for your research.
• Explain significance: Explain the significance of the research you have proposed, and how it will contribute to the field. This will help to justify the need for future research and provide a basis for further investigation.
• Provide a timeline : Provide a timeline for the proposed research , indicating when each stage of the research would be conducted. This will help to give a sense of the practicalities involved in conducting the research.
• Conclusion : Summarize the key points you have made about future research and emphasize the importance of exploring the research questions you have identified.

Examples of Future Research in Thesis

SomeExamples of Future Research in Thesis are as follows:

Future Research:

Although this study provides valuable insights into the effects of social media on self-esteem, there are several avenues for future research that could build upon our findings. Firstly, our sample consisted solely of college students, so it would be beneficial to extend this research to other age groups and demographics. Additionally, our study focused only on the impact of social media use on self-esteem, but there are likely other factors that influence how social media affects individuals, such as personality traits and social support. Future research could examine these factors in greater depth. Lastly, while our study looked at the short-term effects of social media use on self-esteem, it would be interesting to explore the long-term effects over time. This could involve conducting longitudinal studies that follow individuals over a period of several years to assess changes in self-esteem and social media use.

While this study provides important insights into the relationship between sleep patterns and academic performance among college students, there are several avenues for future research that could further advance our understanding of this topic.

• This study relied on self-reported sleep patterns, which may be subject to reporting biases. Future research could benefit from using objective measures of sleep, such as actigraphy or polysomnography, to more accurately assess sleep duration and quality.
• This study focused on academic performance as the outcome variable, but there may be other important outcomes to consider, such as mental health or well-being. Future research could explore the relationship between sleep patterns and these other outcomes.
• This study only included college students, and it is unclear if these findings generalize to other populations, such as high school students or working adults. Future research could investigate whether the relationship between sleep patterns and academic performance varies across different populations.
• Fourth, this study did not explore the potential mechanisms underlying the relationship between sleep patterns and academic performance. Future research could investigate the role of factors such as cognitive functioning, motivation, and stress in this relationship.

Overall, there is a need for continued research on the relationship between sleep patterns and academic performance, as this has important implications for the health and well-being of students.

Further research could investigate the long-term effects of mindfulness-based interventions on mental health outcomes among individuals with chronic pain. A longitudinal study could be conducted to examine the sustainability of mindfulness practices in reducing pain-related distress and improving psychological well-being over time. The study could also explore the potential mediating and moderating factors that influence the relationship between mindfulness and mental health outcomes, such as emotional regulation, pain catastrophizing, and social support.

Purpose of Future Research in Thesis

Here are some general purposes of future research that you might consider including in your thesis:

• To address limitations: Your research may have limitations or unanswered questions that could be addressed by future studies. Identify these limitations and suggest potential areas for further research.
• To extend the research : You may have found interesting results in your research, but future studies could help to extend or replicate your findings. Identify these areas where future research could help to build on your work.
• To explore related topics : Your research may have uncovered related topics that were outside the scope of your study. Suggest areas where future research could explore these related topics in more depth.
• To compare different approaches : Your research may have used a particular methodology or approach, but there may be other approaches that could be compared to your approach. Identify these other approaches and suggest areas where future research could compare and contrast them.
• To test hypotheses : Your research may have generated hypotheses that could be tested in future studies. Identify these hypotheses and suggest areas where future research could test them.
• To address practical implications : Your research may have practical implications that could be explored in future studies. Identify these practical implications and suggest areas where future research could investigate how to apply them in practice.

Applications of Future Research

Some examples of applications of future research that you could include in your thesis are:

• Development of new technologies or methods: If your research involves the development of new technologies or methods, you could discuss potential applications of these innovations in future research or practical settings. For example, if you have developed a new drug delivery system, you could speculate about how it might be used in the treatment of other diseases or conditions.
• Extension of your research: If your research only scratches the surface of a particular topic, you could suggest potential avenues for future research that could build upon your findings. For example, if you have studied the effects of a particular drug on a specific population, you could suggest future research that explores the drug’s effects on different populations or in combination with other treatments.
• Investigation of related topics: If your research is part of a larger field or area of inquiry, you could suggest potential research topics that are related to your work. For example, if you have studied the effects of climate change on a particular species, you could suggest future research that explores the impacts of climate change on other species or ecosystems.
• Testing of hypotheses: If your research has generated hypotheses or theories, you could suggest potential experiments or studies that could test these hypotheses in future research. For example, if you have proposed a new theory about the mechanisms of a particular disease, you could suggest experiments that could test this theory in other populations or in different disease contexts.

Advantage of Future Research

Including future research in a thesis has several advantages:

• Demonstrates critical thinking: Including future research shows that the author has thought deeply about the topic and recognizes its limitations. It also demonstrates that the author is interested in advancing the field and is not satisfied with only providing a narrow analysis of the issue at hand.
• Provides a roadmap for future research : Including future research can help guide researchers in the field by suggesting areas that require further investigation. This can help to prevent researchers from repeating the same work and can lead to more efficient use of resources.
• Shows engagement with the field : By including future research, the author demonstrates their engagement with the field and their understanding of ongoing debates and discussions. This can be especially important for students who are just entering the field and want to show their commitment to ongoing research.
• I ncreases the impact of the thesis : Including future research can help to increase the impact of the thesis by highlighting its potential implications for future research and practical applications. This can help to generate interest in the work and attract attention from researchers and practitioners in the field.

About the author

Muhammad Hassan

Researcher, Academic Writer, Web developer

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• E-bike to the future: Scalability, emission-saving, and eco-efficiency assessment of shared electric mobility hubs

Trinity College Dublin School of Engineering Celebrates Innovative Research on E-Bike Sharing Systems in Dublin

Trinity College Dublin's School of Engineering is excited to announce the publication of an innovative research paper in Transportation Research Part D: Transport and Environment . The paper, titled "E-bike to the future: Scalability, emission-saving, and eco-efficiency assessment of shared electric mobility hubs" , presents a comprehensive framework for evaluating the effectiveness and potential of Dublin’s shared e-bike system. This research is Part of the eHUBS project funded by Interreg North-West Europe and the work was done in collaboration with the ESB.

Authored by Dr Keyvan Hosseini , Dr Tushar Pramod Choudhari , Dr Agnieszka Stefaniec , Professor Margaret O’Mahony , and Professor Brian Caulfield , this study provides critical insights into the future of sustainable urban mobility. The research utilises six months of real-world data to assess the eco-efficiency and scalability of 12 e-bike hubs (eHUBs) across Dublin, employing data envelopment analysis (DEA) and negative binomial regression.

Key Highlights of the Research:

• Framework Development : The team developed a novel framework for appraising the performance of shared electric micro-mobility hubs in urban settings.
• Data-Driven Analysis : Utilising extensive real-world data, the study evaluates the eco-efficiency of eHUBs in Dublin.
• Scalability Insights : The research proposes an e-bike sharing scalability measure using returns-to-scale analysis, highlighting the potential for system expansion.
• Eco-Efficiency Evaluation : The study assesses eco-efficiency based on trip and user characteristics and emission offsets, demonstrating the environmental benefits of shared e-bikes.

Dr. Keyvan Hosseini, who led the project, stated:

"Our findings reveal that shared electric micro-mobility systems like Dublin’s e-bike hubs offer a promising sustainable alternative to car-centric urban transport. The upward trajectory of eco-efficiency indicates substantial potential for system expansion and improved infrastructure."

Trinity College Dublin School of Engineering is grateful to have the support of ESB, Ireland's foremost energy company since its establishment in 1927. Geraldine Moloney, running ESB X_Site - Incubation and Commercialising new ventures, ESB Group, stated:

“ESB is firmly invested in the role innovation and innovative solutions can provide in delivering Net Zero.  This research conducted using the data generated from our investment in piloting shared e-Bikes in the suburbs of Dublin has provided great insight into the potential of shared eMobility solutions to deliver on the Climate Action Plans' aim to reduce our car dependent culture.  The results of the research clearly demonstrate how collaboration across the academic, startup, semi-state and commercial sectors can deliver a sustainable energy transition for all.”

Conclusions and Future Directions:

The paper concludes that integrating shared electric micro-mobility hubs in urban areas dominated by cars can significantly contribute to sustainable mobility. It highlights the necessity of policy reforms, combining discouraging measures against car usage with encouraging policies for accessible and safe cycling.

The study also opens avenues for future research to explore user resistance to adopting sustainable mobility practices and to estimate the economic impact of externalities mitigated by shared micro-mobility hubs.

Brian Caulfield, co-author and project lead, emphasised:

"This research is a crucial step towards understanding and enhancing the efficiency of urban transportation systems. The insights gained will aid policymakers and urban planners in making informed decisions to promote sustainable mobility."

Practical Applications:

• Enhancing Urban Mobility : The framework can be applied to other metropolitan areas to improve shared micro-mobility systems, making urban transport more sustainable.
• Policy Recommendations : The study offers actionable insights for policymakers to encourage the use of shared e-bikes and reduce car dependency.
• Infrastructure Improvements : The research underscores the need for infrastructural enhancements to support the expansion of e-bike sharing systems.

The publication of this paper underscores Trinity College Dublin School of Engineering's commitment to pioneering research and innovation in sustainable solutions for urban transportation.

For more details on this rigorous research, the full paper can be accessed here .

Occasional Reinforced Extinction as a Method for Relapse Prevention: A Critical Systematic Review and Future Directions

• Original Article
• Open access
• Published: 22 June 2024

Cite this article

You have full access to this open access article

• María J. Quintero   ORCID: orcid.org/0000-0002-9420-4121 1 , 2 ,
• Francisco J. López   ORCID: orcid.org/0000-0003-3884-4025 1 , 2 ,
• Miguel A. Vadillo   ORCID: orcid.org/0000-0001-8421-816X 3 &
• Joaquín Morís   ORCID: orcid.org/0000-0002-6283-1577 1 , 2  

Introduction

Extinction is more vulnerable than the original acquisition memory, as relapse phenomena have systematically shown in the literature with different species and procedures. One strategy potentially useful to mitigate relapse is occasional reinforced extinction (ORE). In contrast to a standard extinction procedure, this strategy consists of the inclusion of a gradual and sparse number of conditioned stimulus–unconditioned stimulus pairings within the extinction phase. Here, we provide a comprehensive review of the available literature on ORE.

We conducted a literature search using three databases (Web of Science, Scopus, and PsycInfo) in July 2022, with an additional citation search. We collected data on different variables of interest, like the relapse phenomena being studied, the outcome measures, or the specific effects obtained.

A total of 350 studies were identified from the main database search, including 10 in the review. Five additional studies from the citation search were also included. The final sample consisted of 15 empirical reports. The observed procedural variability makes it difficult to evaluate the effectiveness of ORE to reduce different forms of relapse as the strategy has not consistently shown a general advantage over standard extinction.

The current evidence assessing the effectiveness of ORE does not appear to be consistent, although there are plenty theoretical studies recommending and discussing the potential effectiveness of such technique. Moreover, the lack of conclusive laboratory evidence calls into question how general the potential benefits of its use in clinical settings would be.

Avoid common mistakes on your manuscript.

Anxiety disorders are the most common type of mental disorder in Western societies (see Grillon et al., 2019 ), with a prevalence of up to 25% in the adult population (Baxter et al., 2013 ; Remes et al., 2016 ). These disorders do not only constitute a major health problem for patients, but also come at enormous economic and societal cost. The burden is even greater considering that anxiety disorders are comorbid with other health problems and increase the risk for different mental disorders, such as substance addiction or depression (Grillon et al., 2019 ). Fortunately, exposure-based therapies, a form of cognitive-behavioural therapy (CBT), have empirically demonstrated their effectiveness for most patients suffering from anxiety disorders (Craske & Mystkowski, 2006 ). Exposure-based therapies are a set of techniques in which the patient is repeatedly confronted with an anxiogenic stimulus in the absence of aversive consequences. The aim of this exposure is the reduction of the fear response associated to the anxiogenic stimulus, as well as improving clinical anxiety.

Experimental extinction in the laboratory has been widely used as a model for exposure therapies of anxiety disorders (Graham & Milad, 2011 ; Urcelay, 2012 ) and to understand the origin of different forms of relapse (Vervliet et al., 2013 ). According to this model, fear extinction depends on the development of inhibitory learning (Bouton, 2004 ; Craske et al., 2014 ). The use of experimental laboratory models becomes a relevant tool for trying new techniques that may potentiate inhibitory learning and eventually translate into the improvement of exposure-based therapies (Craske et al., 2014 ; Sewart & Craske, 2020 ; Vervliet et al., 2013 ). In fact, there is ample consensus in the literature that relapse prevention depends crucially on the optimization of inhibitory learning (Craske et al., 2008 , 2014 ; Jacoby & Abramowitz, 2016 ; McGuire & Storch, 2019 ; Weisman & Rodebaugh, 2018 ). Footnote 1 Nevertheless, and although exposure-based therapies are successful in reducing anxiety in the short term, they do not always maintain their effects in the long term, with relapse estimates ranging from 19 to 62% (Craske & Mystkowski, 2006 ).

Several factors have been shown to be implicated in the recovery of the initial problematic response in the laboratory, both in non-human and human conditioning studies. For example, the mere passage of time after the extinction phase may lead to a relapse of the initial anxious response (i.e., the spontaneous recovery effect; Pavlov, 1927 ). Another factor that has been related to relapse is the experience of a stressful situation after extinction, even if that situation is unrelated to the initially anxiogenic stimulus (i.e., the reinstatement effect; Rescorla & Heth, 1975 ). A change in the context in which extinction was initially provided has also shown to promote the renewal of the initial anxious response (i.e., the renewal effect; Bouton & Bolles, 1979 ; see Vervliet et al., 2013 for a review of renewal research). Furthermore, after extinction, later encounters with the initial anxiogenic experience lead to a very rapid relearning, faster than the original learning experience (i.e., the rapid reacquisition effect; Bouton, 2002 ). Importantly, all these different forms of recovery have not only been observed in conditioning studies, but also in the clinical setting after exposure therapy (Boschen et al., 2009 ; Craske et al., 2012 ). Thus, the main current challenge for exposure-based therapies is not so much to achieve anxiety reduction but to prevent the relapse of the pathological anxiety response. In other words, there is ample room for improvement in the efficacy of this successful evidenced-based therapy, with relapse prevention becoming a top priority in this regard (Dunsmoor et al., 2015 ; Vervliet et al., 2013 ).

It is important to note that, although here we refer to the conditioning of fear, these ideas can also be applied to appetitive contexts, in which a neutral cue becomes associated with an event of appetitive or positive significance (for instance, food or drugs). Additionally, although this type of conditioning is less studied in animals and, especially, in humans, it is highly important to advance in the study of certain pathologies, such as substance addiction, gambling, or obesity (Andreatta & Pauli, 2015 ; Quintero et al., 2020 ; Ramnerö et al., 2019 ; Schyns et al., 2020 ). Moreover, equivalent relapse phenomena have been described in appetitive conditioning and, in fact, the relapse prevention strategy studied in this review was first proposed to prevent the relapse of appetitive responses (see Bouton et al., 2004 ).

In recent years, several techniques have been developed from laboratory extinction studies aimed to potentiate inhibitory learning (see Craske et al., 2014 , 2018 , 2022 ; Tolin, 2019 ; Vervliet et al., 2013 ). One of these techniques is the occasional inclusion of reinforced trials during extinction (i.e., occasional reinforced extinction; ORE hereafter). This effect was initially described by Bouton et al. ( 2004 ) and Woods and Bouton ( 2007 ). In a series of animal classical and instrumental conditioning experiments, they found that including some pairings between the conditioned stimulus (CS) and the unconditioned stimulus (US) as part of the extinction procedure could slow down the rate of reacquisition of a previously extinguished response. Following these initial studies, several authors, like Craske et al. ( 2014 , 2018 ), argued that ORE may be a viable and general strategy to enhance inhibitory learning and its retrieval, with a potentially translational value in the clinical domain. Apparently, experiencing the US during extinction may provide some form of resilience to the individual which can be therapeutically beneficial (Krompinger et al., 2019 ).

Different explanations have been proposed for the potential effectiveness of ORE on the mitigation of relapse. According to Bouton et al.’s account ( 2004 ), the initial excitatory association acquired will stay unchanged after extinction. A new inhibitory association between the original CS and the US will be created during extinction, and this second association will be context dependent. This means that it will be engaged only when features of the extinction context are present. Therefore, at a later test phase, conditioned response will be reduced to the extent that the test context resembles the extinction context. The reasoning for this would be that the inhibitory memory will be retrieved and reduce the expression of the original association. Following Bouton et al.’s studies, the preventive effects of ORE should be specific to rapid reacquisition but not to other forms of relapse (Bouton et al., 2004 ; Woods & Bouton, 2007 ). This should occur because reinforced trials in ORE, unlike standard extinction, become part of both the acquisition and the extinction contexts. Reacquisition will be slowed down as reinforced trials introduced after extinction will be able to promote the retrieval of the inhibitory learning developed during extinction. In the case of other recovery phenomena (e.g., spontaneous recovery), the test phase is conducted including only extinction trials. As have been explained, after ORE, the extinction memory will only be retrieved if both reinforced and non-reinforced trials are presented during test.

Gershman et al. ( 2013 ) offer a different explanation for the preventive effects of ORE based on the concept of prediction error. According to their account, relapse prevention depends crucially on the specific distribution of reinforced trials during extinction, so that only a gradual decrease of reinforced trials after acquisition will have a preventive effect. This account assumes that the onset of a standard extinction training produces large prediction errors. The CS strongly predicts the presentation of the US after the initial training, but suddenly this is not the case anymore. They propose that these persistently large prediction errors may serve as a segmentation signal (i.e., a novel state in the environment), demanding the formation of a new inhibitory memory and thus, the original memory remains mostly unmodified. The newly formed inhibitory memory becomes context dependent (see also Bouton, 1993 , 2002 ). However, should these prediction errors be small or infrequent, but still large enough to drive learning, as in ORE, no segmentation would occur, and the original acquisition memory will be weakened. Thus, according to Gershman et al. ( 2013 ), a gradual ORE should have a general preventive effect to all forms of relapse (see Culver et al., 2018 , for other theoretical accounts of ORE general preventive effects).

In recent years, evidence has started to be gathered regarding ORE effects, including experiments with non-human and human participants, using appetitive as well as aversive procedures, and evaluating its effectiveness on different relapse phenomena such as spontaneous recovery, reinstatement, renewal, or rapid reacquisition. Given the rapid accumulation of evidence and the different, even contradicting, pattern of results obtained so far, it is necessary to make a comprehensive and critical review of this evidence. Our objective was to conduct a systematic review of ORE studies to answer the following questions: Is there consistent evidence showing that ORE is effective in reducing the relapse of the conditioned response? Is this relapse prevention effect homogeneous across the different relapse phenomena tested? Under what specific circumstances have these effects been studied (for instance, type of sample, outcome measure, etc.)? What methodological criteria should be taken into account when testing the effectiveness of ORE (for example, distribution of reinforced trials, critical prerequisites to test the effectiveness of ORE, etc.)?

The literature search was conducted in July 2022 following the Preferred Reporting for Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 guidelines (Page et al., 2021 ).

Eligibility criteria

For this review, we considered both laboratory and clinical studies. Given our interest in investigating the potential benefits of an ORE intervention, we included studies conducted with non-human animals and human participants, both in appetitive and aversive conditioning. Given the great heterogeneity of variables, stimuli, and procedures, we decided to include laboratory or clinical studies only if they met the following inclusion criteria:

included an ORE procedure as defined by Bouton et al. ( 2004 ). That is, an extinction phase in which some reinforced trials are presented during extinction. Footnote 2

was conducted using an appetitive or an aversive preparation.

used non-human animal or human samples.

Studies were excluded if they were (i) off topic, (ii) dissertation manuscripts, (iii) study proposals without data or results, or (iv) theoretical articles.

We decided to leave out dissertation manuscripts because they either (a) consisted of computational modelling work, (b) briefly mentioned ORE, or (c) were later published and included in this review. Footnote 3 Additionally, although excluded, we decided to track the number of theoretical works identified during the search process.

Information Sources and Search Strategy

The literature search was performed in two steps. First, MJQ conducted the main search using three databases: Web of Science, Scopus, and PsycInfo. No restrictions in language or publication date were applied. Secondly, MJQ also carried out a citation search to identify studies that were referenced or that cited the studies that were eligible for full-text review in the first step.

The search syntax was developed by taking into consideration the wide variety of terms that have been used to describe the manipulation of interest (ORE). This was achieved by including the different names used in previous papers already familiar to the authors (because of their previous work with this experimental strategy; see Morís et al., 2017 , or Quintero et al., 2022 ). Additionally, extra terms were included (such as “intermittent reinforced extinction”) based on a preliminary literature search conducted on late 2020. We also included the terms related to the field on which we were interested (conditioning and extinction). The final search syntax was as follows:

(“occasional* reinforced extinction”) OR (“partial* extinction”) OR (“partial* reinforced extinction”) OR (“gradual extinction”) OR (“intermittent reinforced extinction”) AND (conditioning) AND (extinction)

Selection Process

After importing the results from the databases on Microsoft Excel ( 2018 ) format, MJQ merged the three different files and revised the resulting references to check for duplicates. After removing them, MJQ and FJL reviewed titles and abstracts of the total results and decided whether to screen the full text. Next, MJQ screened full-text articles for inclusion. After this, MJQ performed an additional search on Google Scholar looking for papers citing the selected reports in the previous search or cited by them. These reports were assessed for inclusion whenever they could be retrieved. If necessary, a second researcher (FJL) was consulted to make the final decision.

Data Collection Process

MJQ designed a data coding sheet after consensus with the other authors was reached on which variables to include, using this document to extract data from eligible studies. This information was reviewed by FJL, JM, and MAV.

We collected data on:

The report: authors, year, and type of publication (laboratory or clinical study).

The study (when applicable): theoretical background, objectives, and hypothesis.

The method (when applicable): sample characteristics (sample, number of participants), setting, stimuli, procedure, dependent variables, or primary outcome measures (cognitive, behavioural, or psychophysiological outcomes, as well as questionnaires), response recovery phenomena assessed or type of test, additional treatments (in the case of clinical studies), and results.

Other relevant information: pre-registrations, availability of data and/or scripts in open repositories, whether sample size was based on a power analysis, and the type of contrast used to test the ORE effect.

Study Selection

We originally found 350 results from the three databases used: 243 from Web of Science, 35 from Scopus, and 72 from PsycInfo. After excluding duplicated articles and other reports for different reasons (namely, translations of the same article), 275 reports were screened. Two hundred and fifty-three of them were excluded based on their titles and abstract. Twenty-two full-texts articles were then assessed for eligibility. However, one of them could not be retrieved since it was a conference abstract. Therefore, full-text review was performed on 21 reports. Five of them did not include an ORE procedure as defined in Bouton et al.’s studies and were excluded. Six of the reports were theoretical and, therefore, excluded. Later, we conducted both reference and citation searching on Google Scholar based on the initially included reports (n = 10). We identified 40 reports and could retrieve 39 of them to assess their eligibility. A total of 21 reports were excluded for not using an occasional reinforced intervention as defined by Bouton et al. ( 2004 ) (n = 15), being thesis dissertations (n = 4), not peer-reviewed works (n = 2) being a study proposal (n = 1) or theoretical articles (n = 12). As already mentioned, it should be noted that (a) one of the papers from the original selection of 10 reports (see Thompson et al., 2018 ) included the results from one of the excluded thesis dissertations, and that (b) although a study proposal was excluded, we included a later study that conducted the proposed intervention and reported the obtained results (see Schyns et al., 2020 ). The final sample consisted of 15 reports. See Fig.  1 for the flow diagram of the study search and selection.

PRISMA 2020 flow diagram of the selection process

Study Characteristics

The fifteen reports included in this review were published between 2004 and 2022. Twelve of them reported the results of laboratory experiments (one of them being a corrigendum for the original publication; see Gershman et al., 2013 , 2021 ), while the remaining three were conducted in clinical contexts (see Jessup & Olatunji, 2022 ; Krompinger et al., 2019 ; Schyns et al., 2020 ). Information about the main characteristics of the laboratory and clinical studies can be found in Tables 1 and 2 .

Effectiveness of ORE: Results from the Laboratory

Different recovery phenomena have been studied when assessing the potential benefit of ORE in the laboratory. However, as can be seen in Fig.  2 , some relapse phenomena (e.g., reacquisition) have been more extensively studied than others (e.g., renewal) and results have not always been consistent. In the following sections, we summarize the main results of this literature.

Effects of an ORE treatment on the different response recovery phenomena. Green circle—response recovery was effectively reduced by ORE. Red circle—response recovery was not reduced by ORE. Grey circle—the response recovery phenomenon was not assessed. Yellow circle—inconclusive results (see the main text for further details)

Animal Studies

Several studies have found that ORE can effectively slow down the rate of reacquisition of the conditioned response. In animals, this effect has been observed with measures such as number of magazine entries (Bouton et al., 2004 ) or number of lever presses (Woods & Bouton, 2007 ). Regarding spontaneous recovery and reinstatement, Gershman et al. ( 2013 ) found that a gradual decrease in the frequency of CS-US pairings during extinction could reduce the return of fear measured as freezing in rats.

Human Studies

van den Akker et al. ( 2015 ), Morís et al. ( 2017 ), and Quintero et al. ( 2022 ) found a slower reacquisition of US expectancy ratings in the occasional reinforced group in comparison to standard extinction. Culver et al. ( 2018 ) found this benefit only on the SCR measure. In contrast, Lipp et al. ( 2021 ) and Thompson et al. ( 2018 ) did not find evidence of such effect in any of the included measures.

Although Culver et al. ( 2018 ) pointed to a reduced recovery of SCR and expectancy ratings, it should be noted that extinction was not asymptotic (e.g., expectancy ratings and SCR levels showed some remaining conditioning at the end of the extinction phase greater in the ORE than in the standard extinction condition, probably due to the differential training), then, these results should be interpreted with caution. Thompson et al. ( 2018 ) found that ORE eliminated spontaneous recovery, in comparison to a standard extinction condition, but only as measured with SCR. Finally, Quintero et al. ( 2022 ) failed to find a prevention or reduction of the spontaneous recovery of expectancy ratings in two experiments.

Lipp et al. ( 2021 ) is, to this date, the only study investigating the effects of occasional reinforcement during extinction on the renewal of the conditioned response. However, they did not find significant effects supporting a beneficial role of this manipulation when compared to the standard extinction group.

Finally, a reduction in the reinstatement of the startle response was found by Shiban et al. ( 2015 ), but these results should be considered carefully, as the sample size for this measure was small (see the section on Statistical and methodological considerations of the ORE literature ). Neither Quintero et al. ( 2022 ) nor Thompson et al. ( 2018 ) could find a preventive effect of ORE on the reinstatement of US expectancy ratings.

Summary of the Results

The results of an occasional reinforced intervention on the reacquisition of the conditioned response tend to be the most consistent, with six out of eight experiments finding a significant effect, both in animals and in humans, and using either appetitive or aversive procedures. Results regarding other relapse phenomena tend to be less reliable, with some tests showing beneficial effects of ORE on the prevention or reduction of spontaneous recovery (Gershman et al., 2013 ; Thompson et al., 2018 ) or reinstatement (Gershman et al., 2013 ; Shiban et al., 2015 ), while others did not (see Quintero et al., 2022 , and Thompson et al., 2018 ). Finally, only one article has studied renewal after ORE, finding no significant results (Lipp et al., 2021 ).

Considering the implications these results may have for the clinical practice, it is fundamental to understand which factors could be responsible for the differences observed across studies. Could it be that different procedural aspects (i.e., recovery phenomena, type of measures, specific procedure…) explain the sometimes-contradictory results? In the following sections, these aspects will be described to further discuss the heterogeneity observed in the ORE literature.

Primary Outcome Measures

As can be seen in Table 1 , a wide variety of outcome measures have been reported within the included literature, ranging from number of magazines entries during CS presentations or the level of freezing in non-human animal studies, to expectancy ratings or skin conductance response (SCR) in human studies. This heterogeneity may hamper the direct comparison between the results of the different studies and the interpretation of the effect of ORE. In fact, although different studies have found significant results on the same relapse phenomenon, they differ in the outcome measure in which those significant results were found. For instance, although both Culver et al. ( 2018 ) and Thompson et al. ( 2018 ) found evidence of a reduced spontaneous recovery, the former did so on SCR and expectancy ratings, whereas the latter only found a benefit on SCR. Footnote 4 Regarding reacquisition, Culver et al. ( 2018 ) could only find an effect on the SCR measure, at odds with other studies (see Morís et al., 2017 ; Quintero et al., 2022 ; van den Akker et al., 2015 ), where the rate of reacquisition was slowed down when measured as expectancy ratings.

Note that the different ORE studies compared the levels of response recovery between groups. However, Dunsmoor et al., following a category conditioning procedure, performed a slightly different comparison, that is, they compared the number of elements from the conditioning and extinction phases that could be recognised at test. Additionally, while Gershman et al. ( 2013 ) also included a long-term memory test, Culver et al. ( 2018 ) conducted a re-test at the end of the task (see Table 1 for more information on the type of test performed in the different studies and the results).

Additionally, some of the included human studies also assessed a series of psychological traits (for example, State-Trait Anxiety Inventory, STAI; Fear of Spiders Questionnaire, FAS; Intolerance of Uncertainty Scale—short version, IUS-12) to control their potential effect on group differences not related to the experimental manipulation rather than to study the effect of individual differences. Of note, all these studies then reported that participants did not significantly differ in the traits measured. See Table 1 for additional information on the reported outcomes within the different empirical articles.

Types of Stimuli

In relation to the nature of the type of CSs used in the laboratory studies, there is also great diversity. The animal studies included within this review used tones or followed an instrumental procedure (measuring lever presses), whereas human experiments used either physical objects (i.e., a children’s jewellery box) or images (such as neutral faces, animals, tools, or geometrical figures). Regarding the USs, the studies used food (i.e., pellets on animal studies; a spoon of chocolate mousse in one of the human studies), electric shocks, an air blast, or an aversive sound. The diversity of stimuli could represent another source of heterogeneity and should be considered, as the type of stimulation may have an influence on the kind of learning that takes place. For instance, whereas some stimuli would promote a stronger emotional response, others would generate weaker responses. This could impact the effectiveness of ORE, obscuring the real effect this procedure may have.

Heterogeneity of the Procedures

Animal studies . Bouton et al. ( 2004 ) reported two experiments. In Experiment 1, animals underwent eight 24-trial sessions during conditioning acquisition, twelve 24-trial sessions during extinction, and one 24-trial session for the reacquisition test. During extinction, the rate of reinforcement was either 1:8 or 2:8, meaning that 1 or 2 out of every 8 trials were reinforced. In their Experiment 2, conditioning consisted of ten 8-trial sessions, while extinction lasted for eleven (Experiment 2—Replication 1) or eighteen (Experiment 2—Replication 2) sessions, with 24 trials each. During these trials, the ratio of CS-US pairings gradually decreased from 1:8 to 1:12, until 1:24. Lastly, the test phase consisted of two 17-trial sessions that evaluated the reacquisition of the conditioned response.

Woods and Bouton ( 2007 ) reported the results from three experiments. All of them used the same general design, with five 30 min sessions during conditioning, eight 60 min sessions for extinction, and a reacquisition test that took place on two 60 min sessions. In their first two experiments, there were two ORE groups that underwent a gradual decrease in the number of reinforced instrumental responses (from a variable interval with an average schedule of 4 min, to a final variable interval with an average schedule of 32 min). These two groups differed on the variable interval schedule they experienced at test. In Experiment 3, the authors decided to keep just one occasional reinforced group, which underwent a training identical to that of the other two experiments for this group.

Gershman et al.’s ( 2013 ) Experiment 1 included three conditioning trials, 24 extinction trials, four long-term memory test trials 24 h after extinction, and four spontaneous recovery test trials 30 days after the previous test. In their Experiment 2, the design was similar, but the reinstatement test took place 24 h after extinction and was followed by the memory test 24 h later. In both experiments, the occasional reinforced group was identical and included a 3:8 reinforcement ratio that was reduced to 2:8 and, finally, to 0:8. Additionally, these experiments included a control condition, namely reverse ORE, where the same number of CS-US pairings was presented but following a gradually increasing fashion.

Human studies . We also observed great differences in the procedures used with human samples. For instance, the number of acquisition trials varies, with studies including five (van den Akker et al., 2015 ), six (Thompson et al., 2018 ), eight (Culver et al., 2018 ; Lipp et al., 2021 ; Morís et al., 2017 , Experiments 2 and 3; Quintero et al., 2022 ), eighteen (Morís et al., 2017 , Experiment 1; Shiban et al., 2015 ), or even forty trials (Dunsmoor et al., 2018 ) per stimulus (CS + or CS−). Note, however, that the procedure used by Dunsmoor et al.’ is slightly different from the other studies included in this review, as it follows a category conditioning preparation (i.e., they use CS categories, such as tools or animals , rather than specific stimuli) that requires the presentation of a large number of trials from each category.

In relation to the extinction design, again, we found substantial variability in the number of trials presented during this phase, as can been seen in Fig.  3 . Additionally, differences were found in the reinforcement schedule used. For instance, although some studies presented a gradually decreasing number of CS-US trials during extinction (Dunsmoor et al., 2018 ; Lipp et al., 2021 ; Morís et al., 2017 , Experiment 3; Quintero et al., 2022 ; Shiban et al., 2015 ; van den Akker et al., 2015 ), some others still included CS-US presentations during the final block of the extinction phase (Culver et al., 2018 ; Morís et al., 2017 , Experiments 1 and 2; Thompson et al., 2018 ). Figure  3 also displays the reinforcement ratio throughout extinction for the different laboratory studies. Footnote 5

Summary of the number of extinction trials and CS-US pairing for the ORE group. Each rectangle represents a block of an equal number of trials, except for Morís et al.’s ( 2017 ), Experiments 1 and 2. For instance, van den Akker et al. ( 2015 ) included 22 extinction trials, therefore, two blocks of 11 trials each. The number within the rectangle specifies how many CS-US pairings were included per block. Numbers in bold represent the total number of extinction trials. In their Experiment 1, Morís et al. ( 2017 ) included 3 non-reinforced trials at the beginning and at the end of the extinction phase, respectively. In their Experiment 2, the number of non-reinforced trials was 2 and 1, respectively

Clinical Studies: Effects of ORE in Therapy

A total of three clinical studies have applied an occasional reinforced intervention in a clinical setting. One of them as a case study with OCD patients (Krompinger et al., 2019 ) and the other two as clinical studies with snake fearful adults (Jessup & Olatunji, 2022 ) and overweight women (Schyns et al., 2020 ). As can be seen in Table 2 , a great variety of measures were assessed, from symptom-related questionnaires (e.g., Yale-Brown Obsessive Compulsive Scale, Y-BOCS, or Eating Disorder Examination Questionnaire, EDE-Q) to expectancy ratings or behavioural tests (i.e., behavioural approach task, BAT).

On these studies, the intervention consisted of exposure experiences where the participants had to occasionally encounter the relevant stimulus or situation. For Krompinger et al. ( 2019 ) this meant that two OCD patients underwent a treatment where they had to confront evidence “confirming their fears” (for instance, one of the patients, who was fearful of causing harm while driving, had to complete a driving exposure where she accidentally knocked over some warning signs that were on the road), taking this experience as an opportunity to learn and recover more easily (i.e., by realizing they can manage the situation despite the unpleasant occurrence). The patients engaged in daily sessions of extinction with response prevention treatment for several weeks, besides attending CBT therapy groups. Symptom progression was assessed weekly and showed a reduction in OCD symptomatology (see Table 2 for more details).

Schyns et al. ( 2020 ) were interested on the effects of cue exposure therapy aimed at strengthening inhibitory learning by violating the CS-US (i.e., food → eating) expectancy. They conducted eight exposure sessions in which participants were exposed to palatable food and instructed to eat a small amount of it once per session and at a variable point. Participants’ expectancies were then measured throughout the session and the researchers evaluated how those exposures affected different relapse-related measures. They compared their results to those from a control condition in which participants received eight sessions (four in person and four via telephone) of psychoeducation on body image, mindfulness, and lifestyle advice. Participants in both groups were evaluated before and after the intervention, as well as three months later. The authors found that the exposure intervention was more effective than the control condition to reduce snacking and binge eating behaviours (see Table 2 for more information).

Finally, Jessup and Olatunji ( 2022 ) exposed participants to four videos of snakes that could be presented alone for 5 min or followed by another video of a snake biting a person (for 20 s) before returning to the initial video. Measuring expectancy ratings and behavioural approach tendencies before and after the intervention, as well as one week later, they found that occasionally reinforced trials during exposure diminished both measures in comparison to the standard exposure group.

As can be seen, the idea underlying these different procedures was also to promote the violation of CS-US expectancies to enhance a stronger inhibitory learning on these subjects. Results from these three studies support a beneficial effect of ORE, with a significant reduction in the problematic symptomatology displayed by the individuals, even in the long term (for instance, Krompinger et al., 2019 , report results from a 6-month follow-up in which reduced symptom levels are maintained.)

Statistical and Methodological Considerations

A lthough we have focused our review on discussing procedural differences within the ORE literature that may explain the sometimes-contradictory results, statistical and methodological aspects should also be taken into account, as they could explain part of the variability observed when investigating the effectiveness of ORE.

The laboratory work discussed in this review varies substantially concerning the number of participants included in each study (see Table 1 ). In human studies, sample sizes tended to be relatively small, with some experiments including 17 participants (see Dunsmoor et al., 2018 ). However, larger samples sizes have also been used, as in Thompson et al. ( 2018 ), Lipp et al. ( 2021 ), or Quintero et al. ( 2022 ), with some of them including up to 157 participants after applying exclusion criteria. Importantly, all of them used a between-subjects design, which have reduced statistical power and limited precision compared to within-participants designs. Footnote 6

Another aspect worth mentioning is the statistical power of the experiments. On average, these studies included 25 subjects per experimental condition. With this sample size, studies are well powered only to detect very large effects (e.g., 80% power to detect a Cohen’s d  = 0.8). Moreover, out of the eleven studies conducted in the laboratory, only two reported power analyses: whereas Quintero et al. ( 2022 ) performed a post-hoc power calculation, Lipp et al. ( 2021 ) used an a priori power analysis to establish the appropriate sample size.

Additionally, in some of those studies, especially the ones measuring physiological variables (namely SCR and startle), the data from some participants were not included in certain analyses (see Fig. 4, in Shiban et al., 2015 ). For example, for the reinstatement test in Shiban et al. ( 2015 ), the contingency and SCR data from 13 participants from the ORE group and 15 from the standard extinction condition were considered, whereas the startle analysis included the data from only 11 participants in the occasional reinforced group and 12 in the standard group. These authors point out that their small sample size should be taken as a limitation. This is especially important considering that small samples data can lead to more variable results.

As for the type of contrasts used in the included studies, we found a wide variety of tests. For instance, while some studies calculated recovery as the difference between response levels at the end of extinction vs. at the beginning of the test, others compared acquisition and test response levels or solely compared the performance of the different groups at test. These differences in the way the ORE effect is calculated, in combination with the large variety of outcome measures (from expectancy ratings to SCR), hamper any formal comparison across studies and the synthesis of the results on a meta-analysis.

Out of the twelve laboratory studies, only Morís et al. ( 2017 ) and Quintero et al. ( 2022 ) made the data and scripts publicly available. However, none of the protocols was pre-registered. Out of the three clinical works, only Schyns et al.’s ( 2020 ) study proposal had been previously published (see van den Akker et al., 2016 , for a detailed description of the protocol as well as a brief section including the proposed statistical analyses).

Extinction has been proposed as the experimental model of exposure therapy, allowing researchers to investigate potential ways to improve the latter with results derived from the laboratory. In fact, several studies have found a correlation between the laboratory and the clinical outcomes (Ball et al., 2017 ; Forcadell et al., 2017 ; Hahn et al., 2015 ; Waters & Pine, 2016 ; see Scheveneels et al., 2021 , for a review on this topic). In recent years, the number of studies investigating potential ways to improve extinction has exponentially increased, with the target at maintaining low levels of the anxiety response in the long term (Craske et al., 2014 ; Vervliet et al., 2013 ).

The sparse inclusion of reinforced trials during extinction has been suggested as an effective strategy to achieve relapse prevention via the enhancement of inhibitory learning (Craske et al., 2014 ). Initially described by Bouton et al. ( 2004 ), ORE has been explored in several laboratory and clinical studies. In this review, we aimed at collecting and performing a critical analysis of the divergent existing literature about this extinction intervention, trying to answer various questions regarding the effect of ORE and the potential conditions that may account for its effectiveness. In the following sections, we will try to answer each of our research questions considering the results of our review.

Is there Consistent Evidence Showing that ORE is Effective in Reducing the Relapse of the Conditioned Response? Is this Relapse Prevention Effect Homogeneous Across the Different Relapse Phenomena Tested?

After conducting the systematic search and applying the inclusion and exclusion criteria, we selected a total of 15 reports, including 12 laboratory and three clinical studies published between 2004 and 2022. By and large, the effects of ORE in the laboratory (see Fig.  2 ) are not homogeneous across the different response recovery phenomena tested in the reviewed studies. The most consistent result seems to be the slowing down of the rate of reacquisition, both in animal and human experiments, although there are some negative results as well. Evidence tends to be less clear when it comes to other less studied recovery phenomena, yielding mixed results regarding the preventive effects of ORE (see Fig.  2 ). Therefore, it is difficult to draw yet a clear conclusion on whether ORE is effective to reduce recovery.

Under What Specific Circumstances Have These Effects Been Studied?

The benefits of ORE are not homogeneous across all relapse phenomena tested. So, which characteristics of these studies may help understand the conditions under which those effects can be obtained?

First, not only the results are contrasting, but the type of outcome measures assessed in the different studies also tends to differ. It should be noted that, although the inclusion of different measures is not uncommon and can even be advisable in the field (see Lonsdorf et al., 2017 ), the ORE literature offers a picture that is difficult to interpret. Not only is ORE not consistently effective to reducing specific recovery phenomena, but the response systems it has an effect on tend to vary across studies (see the Primary outcome measures section for more details). In general, the evidence is mixed, and ORE has not shown to be systematically effective at tackling specific response systems. Unfortunately, it cannot be confirmed whether these differences are telling us something about the dimension of the fear response that ORE could be modifying or if the different results could be solely explained based on procedural or methodological aspects.

It should be noted that it is not unusual to find divergences among the different components of the conditioned response (i.e., verbal, physiological, and behavioural indices). However, even if some components of the response are positively affected by ORE (i.e., preventive effects are observed), the fact that ORE does not influence all response components may eventually cause a more generalised response recovery (Boddez et al., 2013 ). Moreover, it is not clear why ORE should affect certain response systems and not others. A more detailed examination of these discrepancies needs to be performed in the future if the field aim at generating solid and guiding evidence that could be applied to therapy.

Regarding the type of sample, as can be seen in Fig.  2 , animal studies offer consistent evidence supporting the benefit of ORE. However, human studies provide less consistent results (i.e., six experiments with positive ORE effects, six experiments with negative effects, and one experiment with inconclusive results), making it difficult to judge whether ORE is really effective to reduce response recovery.

A wide variety of stimuli has also been used on the different empirical studies, which may have an impact on the learning processes and on the potential comparison among studies. For instance, whereas some stimuli may promote a stronger conditioned response, others may not be adequate to elicit such intense emotional response (either negative or positive). In this case, learning could be hindered, as well as the interpretation of the results, obscuring any benefit of ORE.

What Methodological Criteria Should be Taken into Account When Testing the Effectiveness of ORE?

The heterogeneity among the studies can also be observed in methodological and statistical features. We found a considerable heterogeneity in the procedures used across different studies, especially in terms of number of trials per phase and, more importantly, the type of occasional reinforcement rate applied during extinction. Again, these differences complicate the comparison between studies and might have important implications considering that one of the theoretical explanations of ORE suggests that the original acquisition memory can only be modified by the gradual reduction of the CS-US pairings. Based on associative learning theories (i.e., Rescorla & Wagner, 1972 ), we may expect that the longer the conditioning, the stronger the association between stimuli (other things being equal). Hence, this may lead to differential effects, as it would not be the same to conduct extinction on memories established after an acquisition phase of variable duration. For instance, we would expect the acquisition memory to be stronger and more difficult to modify after twelve than after merely three acquisition trials, and this could potentially explain part of the discrepancies observed in the ORE literature.

Importantly, some of the positive results observed in the ORE literature should be taken with caution. A low number of extinction trials, being some of them CS-US presentations (see Fig.  3 for a summary of the different reinforcement schedules that have been applied), could potentially hinder asymptotic extinction, especially when reinforced trials were still presented on the last trials of this phase. In fact, Culver et al. ( 2018 ) and Shiban et al. ( 2015 ) found a difference between the conditioned response to CS + and CS– even at the end of extinction training. This was noted by Morís et al. ( 2017 ) on their first two experiments, opting for a more gradual decrease in their Experiment 3, in which complete extinction was observed in both ORE and standard extinction groups. Conceptually, an important prerequisite is that extinction must be effectively established before assessing any form of response recovery, especially in order to rule out any difference on conditioned response levels between groups before test that are not due to the experimental manipulation.

Although some studies evaluated various recovery phenomena on different experiments (for example, Gershman et al., 2013 , or Quintero et al., 2022 ), others did not test them independently. We found that those studies evaluated the different phenomena in a sequential way, that is, one test after the other, which might have obscured any preventive benefit of ORE (Culver et al., 2018 ; Lipp et al., 2021 ; Thompson et al., 2018 ) due to a potential carryover effect. For instance, evaluating spontaneous recovery could affect a later evaluation of reacquisition and this latter test would not be a sensible measure for the preventive effects of ORE. In this regard, the experiments that failed to offer support for the slower reacquisition effect after an occasional reinforced training evaluated different response recovery phenomena sequentially. So, even though this manipulation could have been able to slow down the rate of reacquisition, the cumulative effect of previous tests might have undermined the sensitivity to detect it.

Taken together, the differences on various methodological and statistical relevant aspects involved in the study of ORE might have a cumulative detrimental impact on the field, obscuring the potential effect this intervention could have. Moreover, some of them did not ensure minimal critical prerequisites to assess the effectiveness of extinction (i.e., asymptotic response levels prior to the test) or conducted experiments and/or analyses with small sample sizes (see the section on Statistical and methodological considerations of the ORE literature ). These issues hinder a proper comparison across studies, making it more difficult to ascertain the effect ORE could have. Because of this, it can be concluded that, at this time, there is a dearth of clear and systematic laboratory evidence supporting the effectiveness an ORE treatment may have on the reduction of the recovery of the conditioned response.

Recommendations for Future Studies

Although we excluded theoretical articles from the final sample, it should be noted that throughout the literature search we found 18 reports of this kind, that is, articles that mention ORE as a potential strategy to enhance extinction learning and prevent or reduce relapse in the laboratory or within clinical settings (Bautista & Teng, 2022 ; Craske et al., 2014 , 2018 , 2022 ; Dunsmoor et al., 2015 ; Elsey & Kindt, 2017 ; Jansen et al., 2016 ; Keller et al., 2020 ; Kummar et al., 2019 ; Lipp et al., 2020 ; McGuire et al., 2016 ; McGuire & Storch, 2019 ; Monfils & Holmes, 2018 ; Pittig et al., 2016 ; Sewart & Craske, 2020 ; Tolin, 2019 ; van den Akker et al., 2018 ; Weisman & Rodebaugh, 2018 ). Their discussion of the ORE effects varied, going from a simple description of promising results to even recommendations on how to apply it on a clinical setting. From the detailed numbers, it can be concluded that there are more articles highlighting the potential effectiveness of an ORE intervention than actual empirical tests providing evidence of the suggested benefits. This is remarkable considering that the field lacks a standard protocol that could be widely implemented in laboratory or clinical settings and that this type of intervention has already been applied to clinical cases (see Jessup & Olatunji, 2022 ; Krompinger et al., 2019 ; Schyns et al., 2020 ). But even more so when closely investigating the actual effectiveness of ORE on the reduction of relapse and noticing the lack of clear and consistent evidence.

Comparing the results from laboratory and clinical studies, one important factor that could be neglected in the lab would be the suitability of the procedures (for instance, the type of stimuli, the strength of the learning…). It is possible that conditioning and extinction, as studied in laboratory settings, do not really embody the experience that takes place within the clinical context, making it difficult to find strong and clear evidence. In contrast, clinical studies might facilitate the expression of any ORE benefit by conducting research on a more adequate and significant environment for the individuals. It should also be noted that the clinical application of ORE may entail several changes from the laboratory procedure, such as including additional intervention components (i.e., psychoeducation, expectancy violation intervention, multiple contexts exposure, etc.) or a different procedure than the one used in the lab (i.e., including only one reinforced presentation per exposure sessions, as in Schyns et al., 2020 , or only reinforced trials, as in Jessup & Olatunji, 2022 ). Those additional intervention components cast doubts on the idea that ORE is the key element in those positive results, therefore hindering a real interpretation of the effectiveness of this treatment. Moreover, if we consider the translational framework timeline (see Vervliet et al., 2013 ), more systematic evidence is desirable on early stages before advancing on the implementation of ORE with clinical samples. Additionally, individual differences are not being considered when evaluating the potential impact of ORE in the lab given their importance on anxiety and fear (see Lonsdorf & Merz, 2017 ), as well as in addictive behaviours (see Brunault & Ballon, 2021 ).

The already mentioned lack of clear and systematic evidence, as well as the great heterogeneity within the ORE literature, calls for the development of unified protocols (i.e., equivalent number of acquisition and extinction trials, similar reinforcement schedules, ensuring asymptotic extinction, independent study of different relapse phenomena, etc.), consideration of statistical aspects (for instance, including larger samples, an a priori calculation of statistical power or establishing common tests for the effectiveness of ORE to allow comparison across studies), as well as for the adoption of Open Science practices (for instance, pre-registrations or registered reports, making data available, etc.), so that replication is facilitated in the future.

Some limitations of our review should also be noted. First, although we followed the PRISMA 2020 guidelines (Page et al., 2021 ), we did not pre-register the systematic review (for instance, using the OSF or PROSPERO’s servers) nor performed several of the recommended practices (the PRISMA checklist may be found at https://osf.io/6nvta/ ). Additionally, although a second researcher was consulted when necessary, data search and entry was performed by one researcher. The small sample of the laboratory studies included, the different indices used in the studies to calculate response recovery, as well as the great variety of protocols did not allow us to conduct a meta-analysis, which could have provided additional information about the effects of ORE. Lastly, we only included published articles (see Eligibility criteria ), but there may be laboratory and clinical studies that have not been published yet due to publication bias (Dwan et al., 2013 ; Franco et al., 2014 ), and, therefore, were not included in this review. Future studies could try to tackle the necessary statistical approach to conduct a meta-analysis, searching for non-published results.

Conclusions

To sum up, in this review we identified and analysed the existing literature on the effect of ORE. It can be concluded that there has been a substantial variability regarding experimental procedures, not only concerning the phenomena assessed or the measures that were considered, but also regarding number of trials (especially for the extinction phase) and the reinforcement schedule, a key feature of this strategy. Despite all these divergent results and protocols, the picture that emerges is that the effectiveness of ORE has not shown to be systematically superior to standard extinction beyond some beneficial effect to retard the rapid reacquisition of conditioning. Moreover, the limitations observed within the ORE literature call into question how general the potential benefits of its use in clinical settings would be and stress the need to generate high-quality, replicable, and transparent literature. To this day, we do not know the extent of the potential benefit of this strategy, or which factors would determine it (i.e., boundary conditions) and, therefore, further research is needed. Moreover, we should be more cautious when applying ORE to clinical situations considering the lack of consistent laboratory evidence and of a standardised protocol. To the best of our knowledge, this is the first time a systematic review has been conducted on the ORE literature and the results call for the unification of the research protocols and the integration of Open Science practices. To do this, we have suggested that certain methodological and statistical aspects need to be considered to facilitate the replication of ORE studies (see Lonsdorf et al., 2017 ), allowing a better understanding of its value and scope for relapse reduction.

It should be noted that empirical evidence does not always support the inhibitory learning account (see Mason et al., 2023 ). Alternative accounts suggest that extinction promotes the “unlearning” or loss of the original fear memory (see Dunsmoor et al., 2015 , or Gershman et al., 2021 , for more information). Additionally, other non-associative mechanisms may be involved during an extinction training (see Craske et al., 2014 ).

Note that there are other extinction procedures similar to ORE but consisting of including unpaired US presentations (for instance, between trials) instead of presenting proper reinforced trials (see Vervliet et al., 2010 , for an example).

For more information on these reports, see the Search document available at https://osf.io/6nvta/ .

Note, however, that Culver et al.’s results on spontaneous recovery are not clear as the ORE group did not reach asymptotic extinction.

Note that some authors may understand ORE and gradual extinction as different treatments with distinct theoretical implications (see Craske et al., 2022 ). In this review, we consider gradual extinction as a particular case of ORE, in the sense that gradual extinction involves the occasional presentation of the reinforcement during the extinction stage. Consequently, we include studies that follow a gradual distribution of reinforced trials, as well as studies that do not (see the section Heterogeneity of the procedures ). As the field lacks a standard procedure on how to apply ORE, we do not make distinctions between both types of protocols.

Although it may be difficult to implement a within-subject design in this kind of preparations, it would help to maximise the statistical power when using small samples, as this is common in the field. A plausible within-subjects designs could involve the presentation of two different USs (for instance, aversive sounds to the right or the left ear; see Cobos et al., 2022 , for an example). Possibly, this type of design would be more easily implemented in appetitive preparations.

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Acknowledgements

This work was supported by grants UMA18-FEDERJA-051 from Junta de Andalucía, PGC2018-096863-B-I00 from the Spanish Ministry of Science, Innovation, and Universities, and PID2020-118583GB-I00 from Agencia Estatal de Investigación, Spain. María J. Quintero has been awarded with a PhD fellowship from the Spanish Ministry of Science, Innovation, and Universities (FPU Programme, FPU18/00917) and with a postdoctoral grant from the II Plan Propio de Investigación, Transferencia y Divulgación Científica (Universidad de Málaga).

Funding for open access publishing: Universidad Málaga/CBUA. Junta de Andalucía, UMA18-FEDERJA-051, Francisco J. López; Ministerio de Ciencia, Innovación y Universidades, PGC2018-096863-B-I00; FPU Programme, FPU18/00917, María J. Quintero; Agencia Estatal de Investigación, PID2020-118583 GB-I00, Miguel A. Vadillo; Universidad de Málaga, Postdoctoral grant (II Plan Propio de Investigación, Transferencia y Divulgación Científica), María J. Quintero. Funding for open access charge: Universidad de Málaga/CBUA.

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Quintero, M.J., López, F.J., Vadillo, M.A. et al. Occasional Reinforced Extinction as a Method for Relapse Prevention: A Critical Systematic Review and Future Directions. Cogn Ther Res (2024). https://doi.org/10.1007/s10608-024-10497-7

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• http://orcid.org/0000-0002-8814-1021 Hanna Ollila 1 ,
• http://orcid.org/0000-0001-9601-7330 Otto Ruokolainen 1 ,
• http://orcid.org/0000-0002-6614-4782 Tiina Laatikainen 1 , 2 ,
• http://orcid.org/0000-0003-3339-8441 Helena Koprivnikar 3
• and JATC-2 WP9 co-authors
• 1 Department of Public Health , Finnish Institute for Health and Welfare , Helsinki , Finland
• 2 Institute of Public Health and Clinical Nutrition , University of Eastern Finland , Kuopio , Finland
• 3 National Institute of Public Health of the Republic of Slovenia , Ljubljana , Slovenia
• Correspondence to Hanna Ollila, Department of Public Health, Finnish Institute for Health and Welfare, Helsinki 00271, Finland; hanna.ollila{at}thl.fi

The European Union (EU) aims for a tobacco use prevalence of less than 5% by 2040 with its Tobacco-Free Generation goal, aligning with the tobacco endgame approach. In the Joint Action on Tobacco Control 2 (JATC-2) -project, we examined adopted and planned endgame goals and measures as well as preparedness to counter tobacco industry interference in the process. We surveyed key informants in 24 out of 50 countries in the WHO European Region (19 of the 27 EU Member States, MS). Altogether, eight countries (7 EU MS) had official governmental endgame goals, and an additional six EU MS had similar proposals from government, civil society or research entities. Movement towards tobacco endgame was most evident in retail-oriented and consumer-oriented policies. These include restricting the sales of tobacco and related products and raising the age limit above 18 years. Product standards were used especially to regulate flavours but no measures to substantially reduce addictiveness were reported. Market-oriented measures that tap into industry profits were predominantly missing, and countries often lacked concrete tools to prevent industry interference. Respondents’ concerns around tobacco endgame were related to high smoking prevalence in some population groups, non-combustible and new nicotine products, cross-border marketing, political will, challenges with the existing regulations and industry interference. Results indicate both momentum and challenges in adopting and disseminating measures that facilitate achieving tobacco endgame goals. The EU goal can be used to advocate for national endgame goals and measures, and for the strengthened implementation of the WHO Framework Convention on Tobacco Control.

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WHAT IS ALREADY KNOWN ON THIS TOPIC

In the tobacco endgame approach, the focus is shifted from controlling the tobacco epidemic to ending it by reducing use to a minimal level in the population with structural, political and social changes. In the European Union, this is supported by the recently launched Tobacco-Free Generation goal.

Tobacco endgame is well aligned with the WHO Framework Convention on Tobacco Control, which encourages parties to implement measures beyond the convention to better protect human health and obliges them to adopt effective measures to prevent and reduce nicotine addiction besides tobacco consumption.

WHAT THIS STUDY ADDS

While several European countries already have governmental tobacco endgame goals or proposals towards these, there is substantial variation in their definitions, timelines and coverage of tobacco and nicotine products.

Adopted and planned tobacco endgame measures centre around product-oriented, retail-oriented and consumer-oriented policies, such as product standards to reduce appeal, restricting sales and increasing the age limit above 18 years.

HOW THIS STUDY MIGHT AFFECT RESEARCH, PRACTICE OR POLICY

Knowledge sharing facilitates the dissemination of tobacco endgame approach.

More focus is needed on measures that can be expected to have a substantial impact on product availability, appeal and addictiveness.

Concrete tools to prevent and counter tobacco industry interference are needed, as it is seen as a clear challenge in tobacco endgame.

Introduction

In the WHO European Region, encompassing 53 countries including 27 European Union (EU) Member States, 25% of adults use tobacco. 1 This prevalence ranks second highest among the WHO regions, with a relatively slow decline compared with other regions. In 2021, as part of Europe’s Beating Cancer Plan, the EU announced a ‘Tobacco-Free Generation’ goal for the region. 2 While the concept of tobacco-free generation originates in a proposal to limit tobacco sales by year born, 3 the EU goal is defined as less than 5% of the population using tobacco by 2040. The EU goal aligns with the tobacco endgame approach, where the focus shifts from controlling the tobacco epidemic to ending it by reducing use to a minimal level in the population with structural, political and social changes. 4 The EU goal is well justified under the WHO Framework Convention on Tobacco Control (WHO FCTC), which encourages parties to implement measures beyond the convention to better protect human health (Article 2.1) and obliges them to adopt effective measures and cooperate in developing appropriate policies to prevent and reduce tobacco consumption, nicotine addiction and exposure to tobacco smoke (Article 5.2b). 5 Several European countries have already set their national tobacco endgame goals prior to the EU goal. 6 We examine the current status of adopted and planned national goals and measures in the WHO European region, and how these reflect the EU goal among the Member States. We also examine how experts perceive the likelihood of adopting or achieving the endgame goal in their own country, and countries’ preparedness to counter tobacco industry interference in the process.

In the Joint Action on Tobacco Control 2 (JATC-2) project, 7 Work Package 9 (WP9) is tasked to identify national tobacco endgame strategies and forward-looking tobacco control policies, to explore and exchange best practices in the development, implementation and evaluation of these strategies and policies, and to facilitate their development in the European region. The WP9 involves 21 partner organisations from 15 European countries (Belgium, Cyprus, Denmark, Finland, France, Greece, Hungary, Ireland, Italy, Lithuania, Norway, Portugal, Serbia, Slovenia and Spain), with the Netherlands collaborating. As part of this work, we surveyed key tobacco control informants in the WHO European region between 15 September 2022 and 13 January 2023.

Participants

Key informants consisted primarily of national WHO FCTC focal points, who are nominated by their country to participate in the official treaty reporting. Contacting them was made possible through assistance from the WHO FCTC Knowledge Hub on Surveillance and Convention Secretariat. In the absence of a functional contact with the focal point (eg, due to personnel changes), other national tobacco control experts were identified with assistance from JATC-2 partners and the WHO European Office for the Prevention and Control of Noncommunicable Diseases. We excluded Switzerland and Monaco due to lack of contacts, and the Russian Federation due to the suspension of research collaboration because of the war in Ukraine. From each country, one coordinated response was requested if the respondent engaged other stakeholders. The questionnaire gathered information and expert opinions on national-level policies and was, therefore, not subjected to an ethics approval. Respondents gave an informed consent on their participation.

Responses were received from 24 of 50 countries (19 of 27 EU Member states), with response rates of 48% across the region and 70% within the EU. The respondents were from Austria, Azerbaijan, Belgium, Cyprus, Czechia, Denmark, Estonia, Germany, Finland, France, Hungary, Ireland, Italy, Lithuania, Luxembourg, the Netherlands, North Macedonia, Norway, Portugal, Serbia, Slovenia, Spain, Sweden and Uzbekistan. The majority of the respondents were officials from health ministries/departments/directorates in the government. One respondent was from the interior ministry, two from national authorities specialised in addictions or substance use and one from a public health institute. Respondents were contacted back in March 2023 for potential updates, which were received from Uzbekistan. The JATC-2 partners could further update the information on new national policies up to May 2024. Partner updates were provided by Belgium, Finland, France, Ireland, the Netherlands, Norway, Slovenia and Spain.

Questionnaire

The questionnaire assessed the existence of national tobacco endgame goals, their definition, the selected time frame, tobacco or nicotine products covered by the goals and the perceived likelihood of adopting/achieving these goals (from 0=very unlikely to 10=very likely). The reason for the selected response was asked. Furthermore, we inquired about adopted or planned endgame measures and measures to prevent industry interference ( table 1 ). The endgame measures for the questionnaire were identified from earlier reviews. 4 8 In WP9, harm reduction measures are outside the scope of work and were, therefore, not included in the questionnaire. The measures on tobacco industry interference were derived from screening the recommendations of the WHO FCTC Article 5.3 guidelines. Some additional measures of interest to WP9 partners were also added (marked with * in table 1 ). The questionnaire and more details of its development are available in the WP9 indicator compendium at www.jaotc.eu . 9

• View inline

Measures included in the JATC-2 WP9 questionnaire

We describe adopted goals and measures based on respondent-provided details supplemented with publicly available information on the goals and measures (from, eg, governmental and EU websites). For plans or proposals, we disclose country names only if the information is publicly available to prevent industry interference. We present quotes from the experts’ open-ended responses. This article does not seek to present an exhaustive list of endgame goals and measures in Europe but provides examples and experiences, which can help draw an overview of their status and future directions.

Tobacco endgame goals

Official goals adopted or acknowledged by governments.

Altogether eight countries reported official tobacco endgame goals ( table 2 ). These were divided into general population goals without subgroup targets and goals including certain generations or subgroups. Most of the countries are aiming for less than 5% prevalence of use, but three countries aim at no use at all in certain subgroups addressing children or pregnant women. Three countries define their prevalence goals specifically as daily use. All countries except Norway have set a target year between 2025 and 2040. The official definitions focus on smoking or tobacco use, except for three countries that also mention nicotine products or tobacco-related products. Some countries extend the scope of endgame compared with the main definition: Belgium and the Netherlands reported including all tobacco and non-pharmaceutical nicotine products, while France and Norway also reported including heated tobacco products (HTPs) under their smoking targets. Finland and Norway have integrated the endgame goal into the objective of the tobacco control law.

Official tobacco endgame goals among the countries responding to the JATC-2 WP9 questionnaire

Proposals from governmental bodies or other relevant organisations or entities (eg, NGOs, political parties, public health organisations)

Altogether seven countries reported endgame proposals from their countries. In Denmark, the former government introduced a Nicotine-Free Generation goal where no one born since 2010 should start smoking or using nicotine products, 10 but this proposal has not progressed. A strategy for tobacco-free Germany by the German Cancer Research Center, supported by several NGOs and research entities, aims for <5% adult and <2% adolescent prevalence in tobacco and non-pharmaceutical nicotine use by 2040. 11 Additionally, the German government’s strategy for the Sustainable Development Goals contains a goal close to the common endgame prevalence level, namely, of 7% smoking prevalence among youth by 2030. 12 In Italy, scientific societies and independent scientists have allied to advocate for the development of a national tobacco endgame strategy. 13 In Spain, a new comprehensive plan for the prevention and control of tobacco for years 2024–2027 includes a goal to achieve <5% prevalence of daily use among 14–18-year olds. 14 Previously, public health organisations and civil society associations published an endgame declaration calling for a goal of <5% smoking prevalence by 2030 and 2% by 2040 in Spain. 15 Two other countries reported that an endgame proposal exists but is not yet publicly available. One was part of national health strategy discussions, where a goal in line with the EU goal has been proposed. From the second, no details were provided.

Perceived challenges and opportunities in tobacco endgame

Among the respondents from eight countries with official endgame goals, six provided a score for the likelihood of achieving their goal. On a scale of 0–10, the responses were either 6 (three countries) or 7 (three countries), reflecting moderately positive expectations. Concerns were expressed in relation to non-combustible and new nicotine products, differences between population groups, industry interference, cross-border marketing and sales, sustaining the political will and challenges in estimating the impact of the measures ( table 3 ).

Respondents’ reflections on the perceived likelihood of achieving their official governmental tobacco endgame goals (six countries, panel A), and on the perceived likelihood of adopting such goals in their country (12 countries, panel B).

Among 12 of the 16 countries without an endgame goal who provided a score, the expectations of adopting such a goal in their own country varied greatly: from very negative 0–2 (five countries) and somewhat unsure 5 (three countries) to rather positive 7–8 (two countries). Two countries perceived the adoption very likely, scoring 10. Concerns among these countries related to lack of political will, industry interference and problems in current tobacco control processes, shifting the focus to the COVID-19 pandemic, and the current high use of tobacco and related products ( table 3 ). Some countries reported a preference for general addiction or non-communicable disease (NCD) prevention strategies over tobacco control strategies. Having previously established governmental prevalence reduction goals in a cross-cutting way was seen as a strength for moving towards an endgame approach.

Tobacco endgame measures

Independently of whether a national tobacco endgame goal exists, a few measures that can contribute to such a goal were already implemented to some extent. These are presented in table 4 according to the taxonomy set in table 1 and summarised below.

Adopted and planned tobacco endgame measures and forward-looking tobacco control measures among the countries responding to the JATC-2 WP9 questionnaire

Product-oriented measures

The EU Tobacco Products Directive (TPD) and the delegated directive 2022/2100 prohibit characterising flavours in cigarettes, roll-your-own and HTPs, but some countries go beyond this to reduce product appeal with different product standards. Five countries had fully prohibited menthol as an additive that facilitates inhalation in combustibles, and seven countries had prohibited all or most flavours in e-cigarette liquids ( table 4 ). These measures were also planned in some countries, and Finland was processing regulation on nicotine pouch flavours. Plain packaging had been extended from tobacco products to e-cigarette packaging in three countries and was also considered for nicotine pouch packaging in two. Some countries had standardised or were standardising the appearance of individual cigarettes, nicotine e-liquids, e-cigarette refill containers and/or nicotine pouches. Health warnings on individual cigarette sticks were considered in Norway, which had also prohibited imports and sales of waterpipe tobacco, therefore partially addressing a ban on combustibles.

The TPD allows Member States to prohibit a certain category of tobacco or related products if the Commission approves it after considering whether national provisions are justified, necessary and proportionate, and whether they constitute a disguised barrier to trade. Belgium has received approval to prohibit disposable e-cigarettes, and two other countries also have proposals to introduce such a ban. Two countries reported an authorisation scheme for novel tobacco products, where the government authorises or rejects market entry applications. Non-pharmaceutical nicotine products (other than e-cigarettes) are not under TPD and countries regulate their market entry independently. An authorisation scheme for novel nicotine products was reported by two countries. Two countries have prohibited nicotine pouches. One country reported considering a ban on products that do not fall into existing product categories or are placed on the market after a certain date, but no specification was available.

Retail-oriented measures

Some countries reported prohibiting or restricting tobacco or related product sales in retail types or locations related to minors, and Cyprus was planning to restrict points of sales near schools ( table 4 ). Broader restrictions were still rare. New stepwise sales reductions were adopted in two countries, and a substantial reduction in retailers was set to the strategy in Norway but without concrete proposals. Two countries limited tobacco sales to specialist shops, and one country was considering including also e-cigarette sales to these. Hungary has set numerical limits to the density of the specialist tobacco shops. Finland introduced high annual supervisory fees to retail license holders and has had a proposal to prohibit the granting of a retail license to temporary and mobile sales places. France supported the transition of tobacco retailers into other local shops and no longer selling tobacco.

Consumer-oriented, market-oriented and other innovative measures

Most of the proposed endgame measures in these categories were not in place or planned. Plans focused on consumer-oriented measures, mainly age limits of 20 or 21 years, where altogether six countries have had proposals to raise the age of sale above 18. Of these, Ireland already approved in May 2024 a proposal for legislation that will increase the age of sale of tobacco to 21, aiming to be the first EU country to do so. 16 In Norway, a tobacco-free and nicotine-free generation to those born in 2010 is envisaged in a national strategy, but decisions and details on its implementation are awaited. In Denmark, the new prevention agreement proposes prohibiting the import, purchase and possession of nicotine products that are illegal to market in the country. Sweden is utilising excise duty for curtailing industry to set its own retail prices. Five countries have a regulated market model where the state has a monopoly on tobacco sales.

Preparedness to counter tobacco industry interference

While many respondents referred to implementing Article 5.3 of the WHO FCTC, concrete tools to prevent industry interference were often missing. However, some examples of adopted measures were shared. These addressed legislative measures, lobbying registers, a code of conduct/procedure, public disclosure of necessary correspondences, disclosure of lobbying expenses, plans to better regulate production and industry reporting obligations, and ethical guidelines preventing state investments in the tobacco industry ( table 5 ). As for planned measures, three countries were developing guidelines on contact between the industry and governmental organisations, one country was planning to develop a transparency register of contacts between the tobacco industry and government, and another country for the disclosure of the records from necessary interactions.

Regulations and measures to prevent tobacco industry interference among the countries responding to the JATC-2 WP9 questionnaire

Our results indicate both momentum and challenges in adopting and disseminating measures that facilitate achieving the EU Tobacco-Free Generation goal of less than 5% tobacco use by 2040. Almost half of the 27 EU Member States either have already adopted a national tobacco endgame goal or have a proposal for such a goal from the government, civil society or research entities. Outside the EU in the WHO European Region, Norway reported an official tobacco endgame goal. While most of the countries with an official goal aim for a similar <5% prevalence level as the EU goal, the definitions of goals and their specifications in the government documents vary considerably. For some countries, this can also pose challenges in measuring the progress. In Ireland and Sweden, the target year of 2025 is approaching soon, calling for the first comprehensive evaluations of national tobacco endgame strategies in the region. Including tobacco endgame as an objective of tobacco control legislation—like in Finland and Norway—may provide sustainability behind changing governmental programmes or strategies and political will.

In the EU, the Member States have benefitted from common minimum product standards set in the TPD. While several countries already go beyond the TPD to address attractiveness and appeal, no measures that would substantially reduce addictiveness were adopted or planned. To meet the <5% prevalence level by 2040, the TPD should be developed from this perspective in a forward-looking way. The EU has invested substantial effort and resources into the advisory mechanism for the prohibition of characterising flavours. 17 Yet a simplified, effective approach would be to follow the WHO FCTC Article 9 and 10 guidelines to prohibit the use of all ingredients that make tobacco products attractive, including flavouring agents. Furthermore, the EU-level nicotine limits for cigarettes could be lowered to make them less or non-addictive, leading to their gradual phase-out from the market. Based on the evidence, reducing nicotine content in cigarettes to very low levels could improve public health and have benefits across different population groups by decreasing the uptake of regular smoking, decreasing the amount smoked and increasing smoking cessation. 18 Introducing very low nicotine cigarettes on the EU level could be a balanced and justified measure considering the increased product supply caused by the continuous entrance of novel tobacco or nicotine products to the market. These novel products were mainly seen as challenges in tobacco endgame by the respondents, and several countries are already covering nicotine products such as e-cigarettes and nicotine pouches in their endgame goals or measures. This can be seen as a forward-looking approach to respond to tobacco industry strategies, which aim to increase product portfolio and profit, attract new customers and delay and distract from effective control policies. 19 Clear separation between measures to only reduce harm and measures to end the tobacco epidemic may help regulators and policymakers to understand and identify measures that are feasible and likely to produce substantial impact in their local context.

The reported retail-oriented and consumer-oriented measures tended to focus on reducing the sales points by limiting sales to certain retailers and raising the age limit of sales above 18 years. For example, substantial stepwise reductions in retail outlets are beginning to be implemented in the Netherlands and in Belgium. Yet, most countries in the region would still need to introduce retail licensing to effectively control and reduce retail density. 20 In Finland, the licensing with high annual costs has gradually reduced the number of tobacco retailers to approximately a half. However, the number remains high and unequally distributed to more socioeconomically disadvantaged areas—reminding of the continued need to consider the impact of tobacco endgame measures in different population groups. 21 In Hungary, the introduction of state-owned specialist tobacco shops has decreased the density of tobacco shops by 85%, concurring with declining adolescent smoking. 22 The age limits that were under consideration focused on 20 or 21 years. In the European context, where no country yet has implemented an age limit above 18 years for tobacco, this measure could have a substantial impact considering most of the initiation occurs by the age of 20. 23 24 In Europe, Norway was first to publish in March 2023 a goal that children born since 2010 do not use tobacco and nicotine products, but its practical implementation is undecided. 25 The United Kingdom has then moved ahead by announcing in October 2023 that it will become an offence to sell tobacco products to anyone born on or after 1 January 2009. 26 Based on the evidence, the retail- and consumer-oriented measures, especially if combined, can be expected to have a notable impact on tobacco use prevalence and lead to health gains over time. 23 27

The EU goal can be used to support the development of similar national goals. Additionally, it can be used to bring the need for better implementation of the WHO FCTC to the political agenda, connected to the national work for NCD prevention and sustainable development goals. This can be beneficial especially in countries where adopting an endgame goal is not yet seen as feasible in the current tobacco control context. The implementation of the WHO FCTC as well as the capacity for tobacco control needs to be strengthened in Europe. 28 As part of this, countries should look into measures that tap into tobacco industry profits, which are mostly not even planned in the region. Together with the lack of concrete tools to prevent and counter industry interference, this enables the industry to mobilise resources for lobbying and distracting policymaking away from timely and effective measures. Industry interference was identified as a challenge both in adopting and achieving tobacco endgame goals. Better protection is needed even on the EU level, as shown in the recent European Ombudsman investigations. 29 Besides national actions, the EU-level investment and support for the enforcement of tobacco control, together with the regular revision of key directives and recommendations, are essential for achieving the EU goal. An interesting comparison can be found in food safety where the EU audits the application and effectiveness of the laws and controls and provides training to the responsible authorities. 30

Finally, the EU goal can be used to raise awareness of the tobacco endgame approach, leveraging support from civil society and the public. For instance, a study from Ireland showed low awareness but broad support for the local tobacco endgame goal. 31 In the Netherlands, key factors in accelerating tobacco control have been the genesis of a ‘Smoke-free Generation’ movement in the wider society, initiated by the three main national charities, combined with stricter adherence to Article 5.3 of the WHO FCTC and a comprehensive marketing ban. 32 In 2022, several European civil society associations launched a joint European Citizen’s Initiative calling for a broad range of measures including tobacco-free environments and ending the sale of tobacco and nicotine products to citizens born since 2010, but it did not reach enough signatories. 33 To facilitate the dissemination of measures that are likely to have a substantial impact within a reasonable timeframe, knowledge sharing between countries with different tobacco control contexts and approaches is needed. Multinational collaborations such as the JATC-2 can serve as platforms to share best practices and act as vehicles to overcome the barriers of lack of knowledge or political will. A great global opportunity for information exchange presents in the 11th session of the Conference of the Parties of the WHO FCTC in 2025, where an expert group established by the COP10 will present its report on Article 2.1 and forward-looking tobacco control measures. 34 The possibility of shifting the focus from controlling to ending the tobacco epidemic is an important message to convey to policymakers.

Ethics statements

Patient consent for publication.

Not applicable.

Ethics approval

This study gathered only information on national-level policies and expert opinions related to these and was therefore not subject to ethics approval. Participants gave informed consent to participate in the study before taking part.

Acknowledgments

The authors want to thank all the respondents of the questionnaire. The authors are grateful for the support and contributions from all JATC-2 WP9 partners in the development of the questionnaire and provision of feedback to the analysis and reporting of the results as part of the project reporting and deliverable drafting. Further, the authors are grateful for the support from the WHO FCTC Knowledge Hub on Surveillance, the Secretariat of the WHO FCTC and the WHO NCD Office in identifying the contacts for the questionnaire.

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Collaborators Co-authors of the Work Package 9 of the Joint Action on Tobacco Control 2 (JATC-2) -project: Adrián González-Marrón (Group of Evaluation of Health Determinants and Health Policies, Department of Basic Sciences, Universitat Internacional de Catalunya, Sant Cugat del Vallès, Spain), Alessandra Lugo (Department of Medical Epidemiology; Istituto di Ricerche Farmacologiche Mario Negri IRCCS, Milan, Italy), Angeliki Lambrou (Directorate of Epidemiology and Prevention of Non-Communicable Diseases and Injuries, National Public Health Organization (NPHO), Athens, Greece), Anna Mar Lopez Luque (Grupo de Investigación en Control del Tabaco, Institut d'Investigació Biomèdica de Bellvitge (IDIBELL), L'Hospitalet de Llobregat, Barcelona, Spain; Centro de Investigación Biomédica en Red de Enfermedades Respiratorias, (CIBERES), Madrid, Spain; Programa de Prevenció i Control del Càncer, Institut Català d'Oncologia, L'Hospitalet de Llobregat, Barcelona, Spain), Armando Peruga (Grupo de Investigación en Control del Tabaco, Institut d'Investigació Biomèdica de Bellvitge (IDIBELL), L'Hospitalet de Llobregat, Barcelona, Spain, Centro de Investigación Biomédica en Red de Enfermedades Respiratorias, (CIBERES), Madrid, Spain; Centro de Epidemiología y Políticas de Salud, Facultad de Medicina Clínica Alemana, Universidad del Desarrollo, Santiago, Chile), Biljana Kilibarda,(Institute of Public Health of Serbia “Dr Milan Jovanovic Batut”, Belgrade, Serbia), Cristina Lidón-Moyan (Group of Evaluation of Health Determinants and Health Policies, Department of Basic Sciences, Universitat Internacional de Catalunya, Sant Cugat del Vallès, Spain), Daniela Alejandra Blanco-Escauriaza (Group of Evaluation of Health Determinants and Health Policies, Department of Basic Sciences, Universitat Internacional de Catalunya, Sant Cugat del Vallès, Spain), Dolors Carnicer-Pont (Grupo de Investigación en Control del Tabaco, Institut d'Investigació Biomèdica de Bellvitge (IDIBELL), L'Hospitalet de Llobregat, Barcelona, Spain; Centro de Investigación Biomédica en Red de Enfermedades Respiratorias, (CIBERES), Madrid, Spain; Programa de Prevenció i Control del Càncer, Institut Català d'Oncologia, L'Hospitalet de Llobregat, Barcelona, Spain), Efstathios Papachristou (Directorate of Epidemiology and Prevention of Non-Communicable Diseases and Injuries, National Public Health Organization (NPHO), Athens, Greece), Elena Demosthenous (Cyprus National Addictions Authority, Nicosia, Cyprus), Emilia Nunes (General Directorate of Health, Ministry of Health, Lisbon, Portugal), Esteve Fernández (Grupo de Investigación en Control del Tabaco, Institut d'Investigació Biomèdica de Bellvitge (IDIBELL), L'Hospitalet de Llobregat, Barcelona, Spain; Centro de Investigación Biomédica en Red de Enfermedades Respiratorias, (CIBERES), Madrid, Spain; Programa de Prevenció i Control del Càncer, Institut Català d'Oncologia, L'Hospitalet de Llobregat, Barcelona, Spain; School of Medicine and Health Sciences, Campus de Bellvitge, Universitat de Barcelona, L’Hospitalet de Llobregat, Spain), Giulia Carreras (Institute for Cancer Research, Prevention and Clinical Network (ISPRO), Florence, Italy), Giuseppe Gorini (Institute for Cancer Research, Prevention and Clinical Network (ISPRO), Florence, Italy), Helma Slingerland (Ministry of Health, Welfare and Sport, the Hague, the Netherlands), Judit Tisza (National Korányi Institute of Pulmonology, Budapest, Hungary), Lorenzo Spizzichino (Ministry of Health, Rome, Italy), Maria-Alejandra Cardenas (Ministry of Health and Prevention, Paris, France), Maria Karekla (University of Cyprus, Nicosia, Cyprus), Maurice Mulcahy (National Environmental Health Service, Health Service Executive (HSE), Galway Business Park, Dangan, Ireland), Milena Vasic (Institute of Public Health of Serbia “Dr Milan Jovanovic Batut”, Belgrade, Serbia), Salla-Maaria Pätsi (Department of Public Health and Welfare, Finnish Institute for Health and Welfare, Helsinki, Finland), Silvano Gallus (Department of Medical Epidemiology; Istituto di Ricerche Farmacologiche Mario Negri IRCCS, Milan, Italy), Sotiria Schoretsaniti (Directorate of Epidemiology and Prevention of Non-Communicable Diseases and Injuries, National Public Health Organization (NPHO), Athens, Greece), Zsuzsa Cselkó (National Korányi Institute of Pulmonology, Budapest, Hungary).

Contributors Salla-Maaria Pätsi conducted initial analyses from the data. HO analysed the data for this manuscript and wrote the first draft. OR, TL and HK reviewed the first draft. HO developed and revised the following drafts as per the review and contributions from all other authors. All authors approved the final version of the paper. HO is responsible for the overall conduct of the study and the contents of this manuscript.

Funding This work was supported by the European Union’s Health Program (2014-2020) under grant agreement N°101035968. The content of this document represents the views of the authors only and is their sole responsibility; it cannot be considered to reflect the views of the European Commission and/or the European Health and Digital Executive Agency (HaDEA) or any other body of the European Union. The European Commission and the Agency do not accept any responsibility for use that may be made of the information it contains. DCP, AML and EF are partly supported by the Ministry of Universities and Research, Government of Catalonia (grant number: 2021SGR00906) and thank the CERCA programme for institutional support to IDIBELL.

Competing interests None declared.

Provenance and peer review Not commissioned; externally peer-reviewed.

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