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An Interview with Professor Johan Vlaeyen, Thought Leader in the Field of Single-Case Designs

Johan W. S. Vlaeyen is professor at the Universities of Leuven, Belgium and Maastricht, Netherlands. His main research expertise is on the behavioral, affective and motivational mechanisms underlying the transition from common acute aversive sensations to chronic bodily symptoms. His experimental work includes research on the acquisition of pain-related fear and avoidance behavior through direct experience, observational learning, and verbal-symbolic learning. Professor Vlaeyen highly values translational research, and he and his team have developed customized cognitive-behavioral management strategies for individuals suffering chronic bodily symptoms and utilized replicated single-case experimental designs to evaluate the effects of these interventions.

Professor Vlaeyen has published more than 390 papers in international journals and is on the editorial board of the flagship journal Pain, Clinical Journal of Pain, Scandinavian Journal of Pain, Cognitive Behaviour Therapy, and Translational Behavioural Medicine. He is principal author of the book “Pain-related Fear: Exposure-based Treatment of Chronic Pain” (IASP Press, 2012), co-editor of the book “Fordyce’s Behavioral Methods for Chronic Pain and Illness Republished with Invited Commentaries” (Lippincott Williams & Wilkins, 2014).

Professor Vlaeyen received the Pain Award from the Dutch Chapter of the International Association for the Study of Pain (IASP) and was awarded Distinguished International Affiliate of the American Psychological Association, for “unusual and outstanding contributions” to health psychology in 2015. He has an adjunct research professorship at the University of South Australia (Australia) and obtained an honorary doctorate at the University of Örebro (Sweden) for his scientific contributions in the area of health psychology. In 2015, he received prestigious Methusalem structural research funding from the Flemish Government (Belgium) for the research program “Asthenes: from acute aversive sensations to chronic bodily symptoms”.

What attracted you to the field of single-case designs in the first place? Can you tell us about your first project using these methods?

When I was working on my PhD research in the field of chronic pain management and pain psychology, I was struck by the large heterogeneity among individuals with chronic pain. In some individuals pain complaints were strongly associated with feelings of loss and depression, whereas fear of pain and fear of re-injury were key to the maintenance of the pain. When following one individual who presented with sitting and standing intolerance due to pain, I decided to test a behavioral treatment based on successive approximation using a single-case experimental design (SCED) approach. The paper was published in 1989 (Vlaeyen et al., 1989). Of course, at the time, the methodological tools to conduct a SCED were limited. Luckily, things have changed since then!

What are some exciting developments in the field of single-case designs that you have seen throughout your career?

In the last decades we have been able to witness a surge in SCED methodology, which is really exciting. One of these developments are more sophisticated approaches to visual analysis, including novel effect size metrics. Another exciting development is the emergence of inferential statistical methods, including randomization tests and multi-level modeling. Together with numerous online applications for design development and analysis, there are many tools that make the application of SCEDs much more feasible than 10 years ago.

What are some myths about single-case designs you have come across? Where do you think these myths come from and do you think they can be addressed?

One recurrent myth is that single-case designs are not useful because of the limited generalization to other cases. This myth is born of the misconception that group-based designs offer the possibility to generalize. In fact, external validity is a challenge in outcome research in general, regardless of the design being used. Studies using a group-based design offer group means that seldomly represent the data of the individual members of the group. External validity of single-case designs can best be conceived as a gradient of successful replications in other cases, either sequentially or simultaneously. A wider dissemination of single-case design technology is probably the best strategy to abolish this and other myths about single-case designs.

What are some of your most recent applications of single-case designs?

We have performed various studies using SCEDs mostly in the field of pain management. More recently, we also tried to apply a SCED in a lab-based experiment testing the hypothesis that pain can be a classic conditioned response. It was an interesting and challenging experience, and we finally decided on a sequentially replicated AB phase design with 30 participants based on the results from the pilot tests and a power study. We plan to implement this single-case design in a future experiment to test our hypothesis (see De et al., 2022). I believe that applying SCED in fundamental lab-based research might offer new insights into mechanisms at an individual level.

Looking to the future, what are your predictions about future trends/breakthroughs for the field of single-case designs?

My careful prediction is that SCED will become one of the dominant methodologic approaches in the field of evidence-based practice, especially given the excellent fit with the general need for a more personalized care approach.

What do you think the field of single-case designs needs most?

What is currently most needed are better strategies for dissemination and implementation of single-case designs in health care and educational settings. The International Collaborative Network for N-of-1 Trials and Single-Case Designs is already an excellent resource for this (Nikles et al., 2021). Additional activities that can help are the development of Master level courses, workshops, and contributions to international conferences such as symposia.


De, T. K., Madden, V. J., Vlaeyen, J. W. S., & Onghena, P. (2022). Classical Conditioning for Pain: The Development of a Customized Single-Case Experimental Design. Journal of Trial & Error, 2(1).

Nikles J, Onghena P, Vlaeyen JWS, Wicksell RK, Simons LE, McGree JM, McDonald S. Establishment of an International Collaborative Network for N-of-1 Trials and Single-Case Designs. Contemporary Clinical Trials Communications 2021;23:100826.

Vlaeyen JW, Groenman NH, Thomassen J, Schuerman JA, van Eek H, Snijders AM, van Houtem J. A behavioral treatment for sitting and standing intolerance in a patient with chronic low back pain. The Clinical Journal of Pain1989;5(3):233-237.

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