How Useful is Meta-analysis in Evaluating the Effects of Different Psychological Therapies?

Abstract

Shapiro and Shapiro (1982) argue the case that meta-analysis has made, and will increasingly make, an important contribution to the evaluation of the effects of psychological therapies. Briefly stated, they make the following claims for meta-analysis: (1) Meta-analysis provides systematic and quantitative methods for summarizing and integrating the voluminous and diverse literature on psychotherapy. (2) Meta-analysis reduces (eliminates?) the subjective bias that is said to vitiate traditional, qualitative reviews of the literature. Consistent with similar allegations by Smith et al. (1980), Shapiro and Shapiro (1982) suggest that the conclusions drawn in “some” of these traditional reviews “are a function of the assumptions, predispositions and consequent biases of the reviewer.” Meta-analysis, however, is put forward as a distinct alternative to this sorry state of affairs, since it purportedly overcomes these sources of personal and professional bias and results in more objective more accurate evaluations of the evidence. (3) Meta-analysis has “the same superiority over a traditional literature review as that enjoyed by a systematic therapy outcome study over a series of impressionistic case reports.” (4) The advent of objective, quantitative meta-analytic procedures does not abolish the need for traditional literature reviews subjective and qualitative as they might be. The latter have their limited place, just as impressionistic clinical case reports can complement well-controlled experimental outcome studies.