Annu. Rev. Clin. Psychol. 2007.3:1-27. Downloaded from arjournals.annualreviews.org by Ball State University on 01/08/09. For personal use only. ANRV307-CP03-01 ARI 20 February 2007 18:34 Mediators and Mechanisms of Change in Psychotherapy Research Alan E. Kazdin Department of Psychology, Yale University, New Haven, Connecticut 06520-8205; email:
[email protected] Annu. Rev. Clin. Psychol. 2007. 3:1–27 Key Words First published online as a Review in Advance on October 11, 2006 mediators, moderators, mechanisms of psychotherapy, processes and outcomes of therapy, randomized controlled trials, mediation analyses, treatment evaluation The Annual Review of Clinical Psychology is online at http://clinpsy.annualreviews.org This article’s doi: 10.1146/annurev.clinpsy.3.022806.091432 c 2007 by Annual Reviews. Copyright All rights reserved 1548-5943/07/0427-0001$20.00 Abstract There has been enormous progress in psychotherapy research. This has culminated in recognition of several treatments that have strong evidence in their behalf. Even so, after decades of psychotherapy research, we cannot provide an evidence-based explanation for how or why even our most well studied interventions produce change, that is, the mechanism(s) through which treatments operate. This chapter presents central requirements for demonstrating mediators and mechanisms of change and reviews current data-analytic and designs approaches and why they fall short of meeting these requirements. The role of the therapeutic alliance in psychotherapy and cognitive changes in cognitive therapy for depression are highlighted to illustrate key issues. Promising lines of work to identify mediators and mechanisms, ways of bringing to bear multiple types of evidence, recommendations to make progress in understanding how therapy works, and conceptual and research challenges in evaluating mediators and mechanisms are also presented. 1 ANRV307-CP03-01 ARI 20 February 2007 18:34 Contents Annu. Rev. Clin. Psychol. 2007.3:1-27. Downloaded from arjournals.annualreviews.org by Ball State University on 01/08/09. For personal use only. INTRODUCTION . . . . . . . . . . . . . . . . . CONCEPTUAL AND DEFINITIONAL ISSUES . . . . . . . REASONS FOR STUDYING MEDIATORS AND MECHANISMS . . . . . . . . . . . . . . . . . REQUIREMENTS FOR DEMONSTRATING MEDIATORS AND MECHANISMS OF CHANGE . . Multiple Criteria . . . . . . . . . . . . . . . . . General Comments . . . . . . . . . . . . . . . CURRENT STATUS OF RESEARCH ON MEDIATORS AND MECHANISMS . . . . . . . . . . . Examples Where Mediators and Mechanisms are Discussed But Not Well Established . . . . . . . . . . General Comments . . . . . . . . . . . . . . . OVERVIEW OF METHODS FOR STUDYING MEDIATORS AND MECHANISMS IN PSYCHOTHERAPY . . . . . . . . . . . . Statistical Techniques . . . . . . . . . . . . . Design Methods for Studying Mediators and Mechanisms . . . . General Comments . . . . . . . . . . . . . . . PATHS TO IDENTIFYING AND ELABORATING MEDIATORS AND MECHANISMS . . . . . . . . . . . 2 3 3 4 4 6 6 6 8 8 8 10 11 11 INTRODUCTION Several forms of psychotherapy for children, adolescents, and adults produce therapeutic change, as demonstrated in scores of controlled treatment studies (Kazdin & Weisz 2003, Lambert 2004, Nathan & Gorman 2007). The changes can encompass social, emotional, cognitive, behavioral, educational, and physical spheres of functioning. We know well that therapy “works,” i.e., is responsible for change, but have little knowledge of why or how it works. 2 Kazdin Meticulous D