Therapist trainee experience and client outcome: A within-person analysis of hours of experience, client order, initial client distress, and treatment length.

Research does not consistently support the widely held assumption that therapist trainees' skills improve with supervised experience, leading to better client outcomes. The inconsistent findings are limited by methodological constraints. Measures of therapist trainee experience (e.g., training level, years since first client contact) fail to capture clinical experience accurately. Therefore, we operationalized therapist trainees' experience as the total hours of previous client contact under clinical supervision at the time of outcome assessment. We examined how therapist trainees' client contact hours (at the within-person level), client order, initial client distress, and treatment length are associated with client distress in the subsequent week. We used dynamic structural equation modeling to analyze longitudinal data with 1,125 outcome assessments from 192 clients and 45 doctoral-level therapist trainees, collected over 16 years. Therapists received weekly individual supervision and biweekly group supervision. Results indicated that at the within-person level, therapist trainee experience was modestly associated with reduced client distress, particularly for clients with higher initial distress. At the between-person level, therapist trainees' experience had a stronger impact on outcomes in shorter treatment lengths. Findings reveal the complexity of the therapist trainee experience-client outcome relationship and suggest that the effects of therapist trainee experience are contingent on other variables. (PsycInfo Database Record (c) 2026 APA, all rights reserved).