Ten randomised trials (537 participants, ranging from 15 to 136) were included in the review. The average overall quality score was 7.4 (ranging from 5 to 10). Most studies had small sample sizes, ranging from 15 to 45 participants in the active treatment group. Two studies did not include formal measures of treatment fidelity and only one had a sample size calculation. Six studies reported analyses accounting for attrition. It appeared that results were only presented for groups that received psychosocial interventions.
The mean effect size for outcomes categorised as externalising behaviour was 1.12 and for outcomes categorised as internalising behaviour 1.09.
In studies that reported significant psychosocial outcomes, mean effect size for psychosocial functioning was 0.40.
The mean effect size for family-based interventions was 1.8, for individual-based interventions 0.78 and for group-based interventions 0.54.
Average treatment effects were larger for homotypic comorbidity (1.18) than for heterotypic comorbidity (0.57).
Six out of 10 trials included post intervention follow-ups at three, six and 12 months post-intervention. Effect sizes for internalising and externalising behaviours ranged from -0.53 to 0.33 at three months, from -0.15 to 0.48 at six months and from -0.21 to 1.08 at 12 months follow-up.