Efficacy of cognitive–behavioural therapy and other psychological treatments for adult depression: meta-analytic study of publication bias

Background It is not clear whether the effects of cognitive–behavioural therapy and other psychotherapies have been overestimated because of publication bias. Aims To examine indicators of publication bias in randomised controlled trials of psychotherapy for adult depression. Method We examined effect sizes of 117 trials with 175 comparisons between psychotherapy and control conditions. As indicators of publication bias we examined funnel plots, calculated adjusted effect sizes after publication had been taken into account using Duval & Tweedie's procedure, and tested the symmetry of the funnel plots using the Begg & Mazumdar rank correlation test and Egger's test. Results The mean effect size was 0.67, which was reduced after adjustment for publication bias to 0.42 (51 imputed studies). Both Begg & Mazumbar's test and Egger's test were highly significant ( P <0.001). Conclusions The effects of psychotherapy for adult depression seem to be overestimated considerably because of publication bias.