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BackgroundNo meta-analytical study has examined whether the quality of the studies examining psychotherapy for adult depression is associated with the effect sizes found. This study assesses this association.MethodWe used a database of 115 randomized controlled trials in which 178 psychotherapies for adult depression were compared to a control condition. Eight quality criteria were assessed by two independent coders: participants met diagnostic criteria for a depressive disorder, a treatment manual was used, the therapists were trained, treatment integrity was checked, intention-to-treat analyses were used, N⩾50, randomization was conducted by an independent party, and assessors of outcome were blinded.ResultsOnly 11 studies (16 comparisons) met the eight quality criteria. The standardized mean effect size found for the high-quality studies (d=0.22) was significantly smaller than in the other studies (d …