Fourteen RCTs reporting on 16 comparisons were included in the review (3,286 patients, range 45 to 525 patients per comparison). Length of follow-up ranged from two weeks to 18 months.
Compared with controls, depression symptoms in CCBT patients were statistically significantly reduced at intervention endpoint (SMD -0.48, 95% CI -0.63 to -0.33; 16 comparisons; Ι²=71%). Similar results were shown in subgroup analyses of wait list controls (SMD -0.63, 95% CI -0.83 to -0.45; nine comparisons) and controls that received treatment as usual (SMD -0.23, 95% CI -0.37 to -0.09; seven comparisons). The results were not substantially changed in sensitivity analyses that only included only comparisons with neither the Beck Depression Inventory I or II as the primary outcome measure (SMD -0.32, 95% CI -0.48 to -0.17; seven comparisons), comparisons where acceptable attrition rates (<20%) were reported (SMD -0.59, 95% CI -0.85 to -0.34; seven comparisons), comparisons without significant differences in attrition rates between CCBT and control groups at intervention endpoint (SMD -0.50, 95% CI -0.73 to -0.27; nine comparisons) or comparisons reporting modern imputation techniques (SMD -0.34, 95% CI -0.51 to -0.18; eight comparisons).
At long-term follow-up (>6 months), no statistically significant difference in depression symptoms were found between the groups (SMD -0.05, 95% CI -0.19 to 0.09; five comparisons; Ι²=7%).
At intervention endpoint, no statistically significant differences between groups were found in relation to function improvement (SMD -0.05, 95% CI -0.31 to 0.22; 12 comparisons; Ι²=85%). Rates of attrition were statistically significantly higher among CCBT patients compared with controls (RR 1.68, 95% CI 1.31 to 2.16; 16 comparisons; Ι²=55%). Evidence of publication bias was found (Begg's test p=0.009; Egger's test p=0.01; trim-and-fill method SMD -0.32, 95% CI -0.49 to -0.16).