Therapist personality factors as predictors of between-therapist effectiveness differences.

Abundant research across various treatments indicates that therapists can differ in their general, caseload-level effectiveness. However, relatively little is known about therapist factors that predict such "performance" variability. Moreover, most of the limited existing work on this topic has relied on demographic and professional convenience variables, which have demonstrated low predictive power. Thus, it is possible that therapist effectiveness differences would be better explained by personality characteristics that are inescapably present in a clinician's work. Addressing this question, the present preregistered study preliminarily explored whether more versus less effective therapists possess more adaptive personality traits among the "big five," defense style maturity, and psychological mindedness. Data were derived from a randomized clinical trial comparing the efficacy of 16 sessions of cognitive behavioral therapy and psychodynamic therapy for depression (Driessen et al., 2013). Effective sample participants were 142 adult outpatients treated by 32 therapists nested within the treatment condition. Therapists completed multiple personality measures, and patients' depression and global distress symptoms were assessed (via self-report or observer ratings) at baseline and posttreatment. Despite there being significant between-therapist effectiveness differences (on their average patient's posttreatment outcome), multilevel models revealed no significant associations between personality characteristics and such differences on any outcome. It may be that therapists' overall effectiveness has more to do with their transferable actions in the room versus traits they bring into their work. Alternatively, certain traits may predict between-therapist effects but only in specific treatment, patient, and/or cultural contexts that differ from the ones herein. (PsycInfo Database Record (c) 2025 APA, all rights reserved).