A conceptual and methodological analysis of the nonspecifics argument

In support of the inference that psychotherapies produce their benefit by nonspecific means, researchers cite two sets of empirical findings: (a) null results from comparative outcome studies of different psychotherapies, and (b) a statistical relation between the therapeutic alliance and outcome. We show that neither kind of evidence provides strong support for the "nonspecifics" hypothesis. We argue that outcome equivalence does not imply that the same mechanisms produce the outcomes. We also present evidence that for four mental disorders there exists a psychotherapy that exerts its effects through theory-driven, specific means. Finally, implications of the relationship between the therapeutic alliance and outcome are carefully examined, with particular attention to design limitations in studies that have been assumed to support causal inferences. We conclude that the specific effects of psychotherapies may be substantially stronger than is widely believed.