effect of therapist variables on outcomes. The focus has been directed to the interventions and techniques selected and used by the therapist, rather than on the traits of the therapist themselves.
Kim, D. M., Wampold, B. E. & Bolt, D. M. (2006). Psychotherapy Research, 16(2), 161-172.
Data for completer and intent-to-treat samples from the two psychotherapy conditions of the National Institute of Mental Health Treatment of Depression Collaborative Research Program were analyzed to estimate the proportion of variability in outcomes resulting from therapists. Therapists, who were nested within treatments, were considered a random factor in multilevel analyses. These analyses, which modeled therapist variability in several different ways, indicated that about 8% of the variance in outcomes was attributable to therapists, whereas 0% was due to the particular treatment delivered. When therapist effects were appropriately modeled, previously detected differences in efficacy between the two psychotherapy conditions for more severely depressed patients disappeared, as predicted by methodological considerations.
Wampold, B. E. & Brown, G. S. (2005). Journal of Consulting and Clinical Psychology, 73(5), 914-923.
To estimate the variability in outcomes attributable to therapists in clinical practice, the authors analyzed the outcomes of 6,146 patients seen by approximately 581 therapists in the context of managed care. For this analysis, the authors used multilevel statistical procedures, in which therapists were treated as a random factor. When the initial level of severity was taken into account, about 5% of the variation in outcomes was due to therapists. Patient age, gender, and diagnosis as well as therapist age, gender, experience, and professional degree accounted for little of the variability in outcomes among therapists. Whether or not patients were receiving psychotropic medication concurrently with psychotherapy did affect therapist variability. However, the patients of the more effective therapists received more benefit from medication than did the patients of less effective therapists.
Lutz, W., Leon, S. C., Martinovich, Z., Lyons, J. S. & Stiles, W. B. (2007). Journal of Counseling Psychology, 54(1), 32-39
Evidence suggests that a moderate amount of variance in patient outcomes is attributable to therapist differences. However, explained variance estimates vary widely, perhaps because some therapists achieve greater success with certain kinds of patients. This study assessed the amount of variance in across-session change in symptom intensity scores explained by therapist differences in a large naturalistic data set (1,198 patients and 60 therapists, who each treated 10-77 of the patients). Results indicated that approximately 8% of the total variance and approximately 17% of the variance in rates of patient improvement could be attributed to the therapists. Cross-validation and extreme group analyses validated the existence of these therapist effects.
Psychotherapy in General