Six randomised controlled trials consisting of 400 participants were included.
There was no significant heterogeneity across the sample (chi-squared=4.5, df=5, p=0.47).
All studies showed positive effects in favour of cognitive behaviour therapy. In three studies the 95% confidence intervals for the odds ratio did not include 1, indicating a significant difference in favour of cognitive behaviour therapy over the comparison conditions. The pooled odds ratio was 3.2 (95% confidence interval 1.9 to 5.2), suggesting significant improvement in the CBT group over the comparison group.
The rate of improvement after CBT was 62% and the rate of improvement in the comparison group was 36%. Thus for every 100 patients who were treated with CBT there were just 26 extra patients (62-36) who improved because of it. Four patients (95% CI: 3,6) would therefore need to be treated with CBT to gain one additional remission above that arising from the comparison interventions.
Intention to treat analysis: It was assumed that all the withdrawals in the CBT group did not remit and all withdrawals in the control groups remitted. The pooled odds ratio was 2.2 (1.4 to 3.5).
Study quality: The mean quality rating of the CBT studies was 22.7 (max 36). There was a small negative association between the quality rating and the odds ratio (rank r = -0.46; p>0.10), largely because the two trials with lower scores on the quality scale showed the strongest treatment effects. The effect of CBT was still found to be significant when these trials were excluded, giving an odds ratio of 2.2 (95% CI: 1.3, 3.5).