Heterogeneity of Treatment Effects in Trials on Psychotherapy of Depression

Practitioners and researchers alike assume that there is individual variability in the effects of treatments for mental disorders. However, for psychotherapy, up to now this assumption has never been empirically tested. Using a large database of randomized-controlled trials on psychotherapy of depression in adults (306 trials including a total of 51,853 patients), we performed a Bayesian variance ratio metaregression. For the entire sample, we found a 9% higher variance in the intervention groups compared with the control groups. Depending on the depression scale used, this corresponds to a standard deviation of the individual treatment effect of 3 to 4 points. Subgroup analyses revealed that the effect variability of some types of therapy is larger than others. Our results are the first to indicate that patients do benefit differently from psychotherapy. We conclude that there is a sound basis for the paradigm of personalized psychotherapy, which brings about implications for both research and clinical practice.