TRIALS AND TRIBULATIONS IN THE METAANALYSIS OF TREATMENT DIFFERENCES - COMMENT

A fair test of the Dodo bird conjecture chat different psychotherapies are equally effective would entail separate comparisons of every pair of therapies. A meta-analysis of overall effect size for any particul ar set of such pairs is only relevant to the Dodo bird conjecture when the mean absolute value of differences is 0. The limitations of the u nderlying randomized clinical trials and the problem of uncontrolled c ausal variables make clinically useful treatment differences unlikely to be revealed by such heterogeneous meta-analyses. To enhance implica tions for practice, the authors recommend an intensified focus on pati ent-treatment interactions, cost-effectiveness variables, and separate meta-analyses for each pair of treatments.