Therapist effects in internet-delivered cognitive behavior therapy for anxiety and depression.

OBJECTIVE

Several clinical studies have found that therapists differ in their client outcomes, supporting the notion of "therapist effects" in psychotherapy. However, only a handful of studies have investigated therapist effects in internet-delivered cognitive behavior therapy. This study aimed to examine therapist effects in internet-delivered cognitive behavior therapy treatment of anxiety and depression in routine care.

METHOD: Data of 8,145 clients who were treated by 44 therapists were examined. Generalized linear mixed models were performed to identify the presence of therapist effects and the amount of variance attributable to therapists across several outcomes: (a) change in symptoms over time, (b) the occurrence of clinically significant change, (c) treatment completion, and (d) client satisfaction.

RESULTS

Significant therapist effects were observed across all outcomes, indicating that there were differences between therapists in each outcome domain. However, the therapist effects appear relatively modest overall, with therapists explaining 1.5% and 1.4% of variance in change over time in anxiety and depression, respectively, 0.6% and 0.7% of the variance in the occurrence of clinical change in anxiety and depression, respectively, 2.3% of treatment completion, and 1.4% of client satisfaction.

CONCLUSIONS

The findings suggest that there are differences among therapists across a range of outcomes. However, these differences account for a modest proportion of the overall variation in client outcomes. Future research is needed to replicate these findings across different contexts before firm conclusions are drawn. (PsycInfo Database Record (c) 2026 APA, all rights reserved).