The effects of psychological therapies under clinically representative conditions: a meta-analysis.

Recently, concern has arisen that meta-analyses overestimate the effects of psychological therapies and that those therapies may not work under clinically representative conditions. This meta-analysis of 90 studies found that therapies are effective over a range of clinical representativeness. The projected effects of an ideal study of clinically representative therapy are similar to effect sizes in past meta-analyses. Effects increase with larger dose and when outcome measures are specific to treatment. Some clinically representative studies used self-selected treatment clients who were more distressed than available controls, and these quasi-experiments underestimated therapy effects. This study illustrates the joint use of fixed and random effects models, use of pretest effect sizes to study selection bias in quasi-experiments, and use of regression analysis to project results to an ideal study in the spirit of response surface modeling.