Seventeen controlled trials (n=1,248) were included in the review. The number of non-randomised trials appeared to be six according to the data extraction tables, but three according to the text. The overall quality of the studies was reported as suboptimal. Only four studies used concealed allocation and only seven reported blinding assessors. Attrition rates ranged from 0 to 40 per cent.
The mean pooled effect size across 19 comparisons (14 studies) was 0.61 (95% CI: 0.37, 0.85) in favour of psychological interventions compared with control, but there was evidence of moderate to high statistical heterogeneity (Q = 51.20, p<0.001; I2 = 64.84%). One study was identified as an outlier and found to account for a large proportion of the heterogeneity. This was removed from the analysis resulting in an effect size of 0.51 (95% CI: 0.34, 0.68; Q = 24.81; p not significant, I2 = 31.47). Psychotherapy was found to be inferior to other treatments (pharmacological, systematic care and pram walking) with d -0.86 (95% CI: -1.45, -0.28, p<0.01), but only three studies provided data and a relatively high degree of heterogeneity was reported (I2 = 55.5%).
Subgroup analyses indicated that studies using a waiting list control had significantly higher effect sizes than studies using a usual care or other control. A trend also suggested that effect sizes were smaller in studies that failed to used random assignment as compared with those that did.
No evidence of significant publication bias was found and 28 studies were reported to be required to reduce the mean effect size to 0.20.