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The Psychotherapy Dose-Response Effect and Its Implications for Treatment Delivery Services
Nathan B. Hansen, Yale University School of Medicine Michael J. Lambert, Brigham Young University Evan M. Forman, Drexel University

To date, few studies have been published on the doseresponse relationship, but there is general consensus that between 13 and 18 sessions of therapy are required for 50%of patients to improve. Reviewing the clinical trials literature reveals that in carefully controlled and implemented treatments, between 57.6% and 67.2% of patients improve within an average of 12.7 sessions. Using naturalistic data, however, revealed that the average number of sessions received in a national database of over 6,000 patients was less than five. The rate of improvement in thissample was only about 20%. These results suggest that patients, on average, do not get adequate exposure to psychotherapy, nor do they recover from illness at rates observed in clinical trials research. Key words: psychotherapy outcome, dose-response, effectiveness research, efficacy research, clinical significance. [Clin Psychol Sci Prac 9:329–343, 2002]

A large body of psychotherapy research,accumulated over more than 40 years, has convincingly demonstrated the general effectiveness of psychotherapy (Lambert & Bergin, 1994). Additionally, a second generation of psychotherapy research has begun to identify particular treatments that work more or less effectively in specific contexts and populations (Chambless et al., 1996; DeRubeis & Crits-Christoph, 1998; Roth & Fonagy, 1996). Moreover, insome cases, specific parameters have been established regarding the duration of treatment required to achieve meaningful change in the majority of patients.
Address correspondence to Nathan B. Hansen, Yale University School of Medicine, Department of Psychiatry, The Consultation Center, 389 Whitney Avenue, New Haven, CT 06511. E-mail: nathan.hansen@yale.edu.

This wealth of information has thepotential to greatly inform standard clinical practice. However, it appears that psychotherapy research findings have had little impact on everyday clinical practice (Kopta, Lueger, Saunders, & Howard, 1999; Nathan, Stuart, & Dolan, 2000). Further, despite the recognized and frequently addressed importance of psychotherapy research informing public policy in regard to mental health issues (DeLeon,1988, Klerman, 1983; Newman & Howard, 1986; Strupp, 1986), it seems that there are serious difficulties in bridging this gap, not only between researchers and practitioners but also between researchers and policy makers (Speer, 1994; Wiggins, 1992). In this day of accountability and managed health care, the need for clinical research to reach and affect policy makers becomes especially important.For example, concerns have been raised by DeLeon, Vandenbos, and Bulatao (1991) about the current practices of managed health care organizations. These concerns included (1) services are limited as a result of a physician gate-keeping process; (2) unrealistic limits are enforced on the number of sessions provided and/or the amount of money available for service; (3) the quality and appropriatenessof provided mental health service may be inadequate; (4) consumers of mental health services are not provided full information about the services available and, in fact, are usually given positive information while negative aspects of services are withheld; and (5) utilization review is often carried out by unlicensed individuals with little training in mental health issues. Clinical research canhave a direct impact on these areas of concern, but as yet has not been widely cited, even by those who complain about the untoward effects of managed care policies and practices. Cognizant of the difficulty of interpreting and applying clinical research in everyday practice, researchers have

© 2002 AMERICAN PSYCHOLOGICAL ASSOCIATION D12

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