Disentangling the Therapist Effect: Clustering Therapists by Using Different Treatment Outcomes

Abstract Previous studies have shown that therapists’ performance varies, known as therapist effects, and have indicated that therapists who excel in one treatment outcome may not necessarily be effective in other outcomes. This observational naturalistic study aimed to enhance our understanding of therapist effects and the assessment of therapists’ performance in different areas. The study included 68 therapists and 5,582 clients from a large mental health facility. Information about their learning activities was available for a subsample of 49 therapists. Separate multilevel analyses were conducted for treatment outcomes, including case mix-corrected OQ-45 change scores, dropout rates, referrals to other facilities, treatment duration, and client satisfaction ratings. A hierarchical cluster analysis was performed to identify groups of therapists based on their performance across various treatment outcomes. Additionally, differences in therapist characteristics among the clusters identified were examined. Therapist effects varied across different outcomes, ranging from small (2.6% for OQ-45 change) to moderate (6.5% for number of sessions). The cluster analysis revealed four distinct clusters of therapists with specific profiles. They had performance differences in certain areas but not in others. This exploratory study supports the notion that therapists exhibit diverse profiles regarding treatment outcomes. These findings are significant for future investigations of therapist effects that aim to identify the characteristics of effective therapists and in the context of personalizing treatment for clients.