Therapist effects vary significantly across psychological treatment care sectors

Psychological intervention outcomes depend in part on the therapist who provides the intervention (a therapist effect). However, recent reviews suggest that therapist effects may vary as a function of the context in which care is provided and therefore should not be generalized beyond that context. This study statistically analysed therapist effect differences between care sectors delivering psychological interventions. The sample comprised routine clinical data from 26,814 patients (69% female; mean age 38) and 466 therapists in five care sectors: primary care, secondary care, university, voluntary, and workplace. Therapist effects were analysed using multilevel models and Markov chain Monte Carlo credible intervals. The therapist effect was significantly larger in primary care (8.4%) than in any other sector (1.1%-2.3%) except secondary care (4.1%), after controlling for explanatory baseline and process variables as well as accounting for differences between clinics. There were no other significant differences detected between care sectors. These findings support the hypothesis that differences in effectiveness between therapists vary depending on the context in which psychological treatment is provided. Differences in relative therapist impact can vary by a factor of 4-8 across treatment sectors. This should be considered in the application of research evidence, treatment planning, and the design and delivery of psychological care provision.