Disentangling between- and within-patients effects of emotion regulation on outcome in naturalistic psychotherapy.

OBJECTIVE The aim of this study was to disaggregate the between-patient and within-patient effects of emotion regulation (ER) on treatment outcome and explore relevant trait-like moderators of the within-patient effects. METHOD Three hundred thirty-nine patients with heterogenous clinical conditions were admitted to psychotherapy at a clinical center. During the intake evaluation, patients completed the Inventory of Interpersonal Problems, the Outcome Questionnaire 30, and the State Difficulties of Emotion Regulation Scale. Subsequently, patients responded to the Outcome Questionnaire 30 and State Difficulties of Emotion Regulation Scale every session for the initial five sessions, followed by assessments every two sessions until the 15th session and then every four sessions until the end of treatment. RESULTS Multilevel models revealed significant between- and within-patient effects of ER on clinical distress. That is, patients with lower average levels of ER difficulties showed greater benefit from treatment, and lower ER difficulties over the course of treatment were associated with lower clinical distress. Furthermore, interactive models demonstrated that lower average levels of ER throughout treatment and fewer interpersonal problems at the beginning of treatment were associated with better treatment outcome. CONCLUSION These findings provide evidence supporting the role of ER as a mechanism of change. The interaction between trait-like components and state-like fluctuations of ER suggests a capitalization model for the role of ER in psychotherapy. (PsycInfo Database Record (c) 2024 APA, all rights reserved).