Does baseline severity interact with the effects of psychotherapy for depression? A meta-analytic review

Introduction It is not yet clear whether baseline severity is associated with the effects of psychotherapies. We examined baseline severity at the study level in a large sample of randomized controlled trials comparing psychotherapies against a control condition for the treatment of depression. Methods We used an existing large database of randomized trials comparing psychotherapies for depression with control groups (www.metapsy.org). We converted baseline severity scores across different depression measures into a common metric. We ran bivariable and multivariable meta-regression analyses to examine the association of effect sizes with baseline severity. We also examined response rates in treatment and control conditions. Results We included 387 randomized trials (463 comparisons; 47,315 patients). The pooled effect size of the psychotherapies was g = 0.77 (95 % CI, 0.70; 0.84). In the main analyses, we found a highly significant association between the effect size and baseline severity (bivariable coefficient: 0.024 (SE = 0.006; p