Trials and tribulations in the meta-analysis of treatment differences: Comment on Wampold et al

A fair test of the Dodo bird conjecture that different psychotherapies are equally effective would entail separate comparisons of every pair of therapies. A meta-analysis of overall effect size for any particular set of such pairs is only relevant o the Dodo bird conjecture when the mean absolute value of differences i 0. The limitations of the underlying randomized clinical trials and the problem of uncontrolled causal variables make clinically useful treatment differences unlikely to be revealed by such heterogeneous meta-analyses. To enhance implications for practice, the authors recommend an intensified focus on patient-treatment interactions, cost-effectiveness variables, and separate meta-analyses for each pair of treatments. Wampold et al. (1997) examined studies that directly compared "bona fide " treatments [i.e., treatments hat "were based on psy-chological principles, were offered to the psychotherapy commu-nity as viable treatments (e.g., through professional books or man-uals), " and "were delivered by trained therapists " (p. 205; with at least a master's degree)] to patients with bona fide clinical problems. The results of their analyses are consistent with thos