Interpersonal impacts mediate the association between personality and treatment response in major depression / Sarah S Dermody, Lena C Quilty, R Michael Bagby

Personality, as characterized by the Five-Factor Model, predicts response to psychotherapy for depression. To explain how personality impacts treatment response, the present study investigated patient and therapist interpersonal processes in treatment sessions as an explanatory pathway. A clinical trial was conducted in which 103 outpatients (mean age: 41.17 years, 65% female) with primary major depressive disorder completed 16-20 weeks of cognitive-behavioral or interpersonal therapy. Before treatment, patients completed the Revised NEO Personality Inventory to assess personality domains (neuroticism, extraversion, openness-to-experience, agreeableness, and conscientiousness). After 3 and 13 weeks, patient interpersonal behavior was rated by the therapist and vice versa to determine levels of patient and therapist communal and agentic behaviors. Depression levels were measured before and after treatment. Structural equation modeling supported that patients' interpersonal behavior during therapy mediated the associations between pretreatment personality and depression treatment outcome. Specifically, extraversion, conscientiousness, and neuroticism (inverse) predicted higher levels of patient communion throughout treatment, which was in turn associated with improved treatment outcomes. Furthermore, patient agreeableness was inversely associated with agency throughout treatment, which was linked to poorer treatment response. Therapist interpersonal behavior was not a significant mediator. Results suggest that patient interpersonal behavior during treatment may be one way that patient personality impacts clinical outcomes in depression. Results underscore the clinical utility of Five-Factor Model domains in treatment process and outcome.

Psychology