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News and Views
October 2002

Mediators and Moderators of Treatment Effects in Randomized Clinical Trials

Author Affiliations

From the Department of Psychiatry and Behavioral Sciences, Stanford University, Stanford, Calif (Drs Kraemer and Agras); Department of Psychology, Rutgers University, New Brunswick, NJ (Dr Wilson); and Department of Psychiatry, Oxford University, Oxford, England (Dr Fairburn).

Arch Gen Psychiatry. 2002;59(10):877-883. doi:10.1001/archpsyc.59.10.877

Randomized clinical trials (RCTs) not only are the gold standard for evaluating the efficacy and effectiveness of psychiatric treatments but also can be valuable in revealing moderators and mediators of therapeutic change. Conceptually, moderators identify on whom and under what circumstances treatments have different effects. Mediators identify why and how treatments have effects. We describe an analytic framework to identify and distinguish between moderators and mediators in RCTs when outcomes are measured dimensionally. Rapid progress in identifying the most effective treatments and understanding on whom treatments work and do not work and why treatments work or do not work depends on efforts to identify moderators and mediators of treatment outcome. We recommend that RCTs routinely include and report such analyses.