How much psychotherapy is needed to treat depression? A metaregression analysis

Background: Although psychotherapies are effective in the treatment of adult depression it is not clear how this treatment effect is related to amount, frequency and intensity of therapy. Methods: To fill this gap in knowledge, the present metaregression analysis examined the association between the effects of psychotherapy for adult depression and several indicators of amount, frequency and intensity of therapy. The analysis included 70 studies (92 comparisons) with 5403 patients, in which individual psychotherapy was compared with a control group (e.g. waiting list, care-as-usual). Results: There was only a small association between number of therapy sessions and effect size, and this association was no longer significant when the analysis adjusted for other characteristics of the studies. The multivariable analyses also found no significant association with the total contact time or duration of the therapy. However, there was a strong association between number of sessions per week and effect size. An increase from one to two sessions per week increased the effect size with g=0.45, while keeping the total number of treatment sessions constant. Discussion: More research is needed to establish the robustness of this finding. Based on these findings, it may be advisable to concentrate psychotherapy sessions within a brief time frame.