Clinical Psychology and Psychotherapy Clin. Psychol. Psychother. 12, 417–426 (2005) Copyright © 2005 John Wiley & Sons, Ltd. Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/cpp.473 The Effect of Therapist Experience on Psychotherapy Outcomes Scott C. Leon, 1 * Zoran Martinovich, 2 * Wolfgang Lutz 3 and John S. Lyons 2 1 Department of Psychology, Loyola University Chicago, IL, USA 2 Department of Psychiatry, Division of Psychology, Northwestern University Medical School Chicago, IL, USA 3 Department of Psychology, University of Berne, Switzerland The present study investigates the impact of therapist experience treating clients on outcomes for future clients with similar demo- graphic and clinical characteristics. Prior research has consistently failed to demonstrate that therapists with more experience (i.e. years of experience working with patients) are more effective than thera- pists with less experience. However, the literature is often criticized for failing to control for variables such as the amount and type of patients treated across therapist comparisons. The samples for the current study are taken from a larger national sample of 2366 outpa- tients receiving psychotherapy from across 92 therapists. The overall sample includes 83 matched pairs of patients across 83 of the 92 orig- inal therapists. Results indicate that therapists may be able to use prior experience with a patient to enhance future outcomes as long as latter patients are clinically and demographically similar and enter treatment shortly after the initial patient. Implications for how ther- apists are trained and use experience are discussed. Copyright © 2005 John Wiley & Sons, Ltd. * Correspondence to: Scott C. Leon, Loyola University Chicago, Department of Psychology, 6525 North Sheridan, Chicago, IL 60626, USA. E-mail: sleon@luc.edu As part of the classic meta-analysis by Smith and Glass (1977) demonstrating the overall effective- ness of psychotherapy, these researchers examined whether years of experience as a therapist corre- lated with outcome. The authors found that years of experience correlated -0.01 with effect size (Smith & Glass, 1977). In their 1980 meta-analysis of 485 studies, the correlation was again zero (Smith, Glass, & Miller, 1980). Shapiro and Shapiro (1982) conducted another meta-analysis in response to the criticisms made of the meta- analyses of Smith et al. Sample therapists had an average of three years of experience. Despite improvements in their meta-analysis, these researchers again failed to find a correlation between years of experience and effect size. After multiple studies suggesting that experience plays a minimal to non-existent role in psy- chotherapy outcome and the inability to effectively criticize this literature (Nietzel & Fisher, 1981), A fair amount of research has now accumulated demonstrating that the therapist variable plays a role in psychotherapy outcome (Luborsky et al., 1986; Crits-Christoph & Mintz, 1991; Crits- Christoph et al., 1991). Specific variables such as therapist age, sex, race, therapeutic alliance, direc- tiveness, locus of control, dominance and coping style have all been examined and shown to have variable relationships with outcome (Beutler et al., 1997). One frequently provocative area in the history of this research involves the effect of ther- apist experience (i.e. years in practice) on psy- chotherapy outcomes.