Mechanisms of action in youth psychotherapy

Background: In this review, we address a basic, but unanswered, question about psychosocial interventions for youth: How does psychotherapy work? Methods: We propose a framework for using mediation analysis to answer this question, and we review the youth therapy outcome literature for evidence on mediating mechanisms. We focus our review on clinical trials of empirically supported treatments for youth anxiety, depression, and disruptive behavior ( N = 67). Results: Contrary to previous reports indicating that potential mediators are rarely assessed, 63% of the studies included measures of potential mediating mechanisms in their designs. Across treatment domains, percentages ranged from 22% of the studies of learning‐based interventions for anxiety (i.e., systematic desensitization, modeling, and reinforced practice) to 91% of parent training investigations. Despite the rather extensive assessment of potential mediators, only six studies included any attempt to use the measures in a formal mediation test. Thus, despite the positive effects of treatments and surprisingly ample assessment of mediators, we still know remarkably little about how youth psychotherapies work. Conclusions: We note common problems that hampered mediation testing (e.g., the design of many trials made it difficult to determine the temporal order of change in the mechanism and outcome), and we offer recommendations for improving study design to better assess mechanisms of therapeutic action. We also note the need to test mediation among referred youth treated in representative practice settings to complement the laboratory‐based evidence on therapy mechanisms that prevails to date.