Big Five personality dimensions and their association with depressive symptom severity over the treatment course.

Personality traits and depressive symptoms are closely related, yet their coordinated change during treatment remains insufficiently understood. We examined change in Big Five scores and depression during inpatient care and tested whether personality trait expression was associated with symptom-specific depressive change. In this naturalistic study, 334 inpatients with affective or psychotic disorders at a German University Hospital completed Beck Depression Inventory and Big Five Inventory-2-XS across three to five assessments. Coordinated change in depression severity and personality scores was examined using bivariate latent growth models. To capture symptom-level heterogeneity, proportional-odds ordinal mixed-effects models were fitted for each BDI item using average personality scores across treatment as moderators. Depression severity decreased over treatment. Growth models showed coordinated change between depression and several personality trait scores: reductions in Neuroticism and increases in Agreeableness, Conscientiousness, and Extraversion were associated with greater reductions in depression severity. At the symptom level, higher average Neuroticism was associated with slower improvement across a broad range of affective, cognitive, somatic, and functioning-related symptoms. Higher average Agreeableness and Extraversion were associated with faster improvement in selected symptoms, while Openness showed limited symptom-specific associations and Conscientiousness showed no significant moderation effects. Self-reported personality trait scores and depression show coordinated change during inpatient treatment. Symptom-level analyses suggest that depressive symptom trajectories differ according to average personality trait expression across treatment. These findings highlight the potential value of integrating personality assessment with symptom-level monitoring, while underscoring that the observed associations are non-causal and should not be interpreted as baseline prediction.