The Role of Efficacy vs. Effectiveness Research in Evaluating Psychotherapy

A sound base of evidence for different kinds of psychotherapy is a fundamental prerequisite for adequate access to treatment. The present article addresses the question of what kind of evidence is required to demonstrate that a specific method of psychotherapy works. Referring to recent conceptualisations of the logical structure of scientific theories, the authors argue that randomised controlled trials (RCTs) and effectiveness studies refer to different domains of intended applications. In RCTs the efficacy of a treatment under controlled experimental conditions is tested, whereas in effectiveness studies the outcome of a treatment under the conditions of clinical practice is examined. Accounting for the different domains of intended applications has several important implications. These implications refer to methodological questions of research (e.g. internal and external validity, study design type), but also the possibility of transferring results from experimental to field settings, and the criteria for evaluating the evidence-base of treatments. They also address the important question of the degree to which the presently available forms of psychotherapy can be regarded as evidence-based. The considerations presented in this article primarily refer to psychotherapy; however, they are also relevant to the evidence-based treatment approach in general.