An analysis of psychotherapy versus placebo studies

Abstract

Smith, Glass, and Miller (1980) have reported a meta-analysis of over 500 studies comparing some form of psychological therapy with a control condition. They report that when averaged over all dependent measures of outcome, psychological therapy is. 85 standard deviations better than the control treatment. We examined the subset of studies included in the Smith et al. metaanalysis that contained a psychotherapy and a placebo treatment. The median of the mean effect sizes for these 32 studies was. 15. There was a nonsignificant inverse relationship between mean outcome and the following: sample size, duration of therapy, use of measures of outcome other than undisguised self-report, measurement of outcome at follow-up, and use of real patients rather than subjects solicited for the purposes of participation in a research study. A qualitative analysis of the studies in terms of the type of patient involved indicates that those using psychiatric outpatients had essentially zero effect sizes and that none using psychiatric inpaticnts provide convincing evidence for psychotherapeutic effectiveness. The onty studies clearly demonstrating significant effects of psychotherapy were the ones that did not use real patients. For the most part, these studies involved small samples of subjects and brief treatments, occasionally described in quasibeliavioristic language. It was concluded that for real patients there is no evidence that the benefits of psychotherapy are greater than those of placebo treatment.