Twenty-four RCTs were included in the review (n=1,851 participants).
Cognitive-behavioural therapy in treatment-seeking groups (n=711 participants, 16 RCTs) had a mean effect size of 1.40 (95% CI 1.00 to 1.81). Cognitive-behavioural therapy in at-risk groups (n=1,140 participants, eight RCTs) had a mean effect size of 0.74 (95% CI 0.39 to 1.08). Statistically significant heterogeneity among trials was observed for both types of participants (p<0.001 for both).
Publication year was not statistically significantly related to effect size for either type of participant. Control condition did not moderate effect size in at-risk groups, but in treatment-seeking groups waiting-list control conditions showed larger effect sizes than psychological control conditions. Effect size varied as a function of therapist contact in treatment-seeking groups, but not for at-risk groups.
There did not appear to be evidence of publication bias.