The Quest for Causality in Psychotherapy Research

This commentary on the article by Frankl, Wennberg, Berggraf and Philips (2020) focuses on methodological aspects of case studies versus group designs in psychotherapy research. Experimental case study designs such as ABAB design and multiple baseline design have a long tradition within behavior therapy. These research designs are especially useful for testing newly developed therapy methods and investigating the effectiveness for treatment of rare disorders. However, experimental case study design is most appropriate for single-component treatments for patients with one circumscribed problem. Randomized controlled trials (RCTs) are considered as the gold standard for testing and establishing the efficacy of a particular therapy method for a particular problem. However, the RCT design also bears some methodological shortcomings, such as low external and construct validity, simplistic epistemological assumptions, and only being able to establish average causal effect (thus not giving the clinician clear guidelines on how to work with individual patients). Rigorous process research is useful for identifying change mechanisms in psychotherapy. Finally, pragmatic case studies have a great potential of increasing our knowledge about psychotherapy and its effectivess. This potential could be increased even further if pragmatic case studies integrated some methods from process research and if the results from multiple case studies were analyzed together in meta-syntheses.