Association of Personality Traits with Rumination Improvement Following Cognitive Behavioral Therapy in Major Depression: An Observational Study

Sachiko Noda¹Atsuo Nakagawa²Satoshi Umeda³Mizuki Amano¹Waka Nogami²SAKAE IHARA¹Yuki Kobayashi¹Mire Ozawa Kinouchi¹Ryo Takemura⁴Hiroyuki Uchida¹Nariko Katayama^1,5*

• ¹Department of Neuropsychiatry, Keio University School of Medicine, Tokyo, Japan
• ²Department of Neuropsychiatry, St. Marianna University School of Medicine, Kawasaki, Japan
• ³Department of Psychology, Faculty of Letters, Keio University, Tokyo, Japan
• ⁴Clinical and Translational Research Center, Keio University Hospital, Tokyo, Japan
• ⁵Health Center Mental Health Division, Keio University, Tokyo, Japan

Introduction: Cognitive behavioral therapy (CBT) is effective for major depressive disorder (MDD), yet individual responses vary. Personality may relate to outcomes, but its role in brooding rumination during CBT remains unclear. This study tested whether baseline personality traits are associated with brooding change in patients with MDD receiving CBT. Methods: In this prospective observational cohort, 75 outpatients were allocated to CBT + treatment-as-usual (TAU) (n=33 baseline; n=30 longitudinal) or TAU alone (n=42; n=38) based on clinical course and preference. The Ruminative Responses Scale (RRS) brooding subscale and the 17-item Grid-Based Hamilton Depression Rating Scale (GRID-HAMD17) were assessed at baseline and 16 weeks; the Temperament and Personality Questionnaire (T&P) was assessed at baseline. Multiple linear regressions within each group examined associations between baseline traits and brooding change, adjusting for sex, baseline brooding, and baseline GRID-HAMD17. A trait-wise single-predictor sensitivity analysis used the same covariates. Results: Both groups demonstrated significant within-group improvements. Hedges’ g (95% CI): CBT—brooding 0.48 (0.11–0.85), GRID-HAMD17 1.07 (0.63–1.50); TAU—brooding 0.84 (0.47–1.21), GRID-HAMD17 1.46 (1.01–1.91). In CBT, higher anxious worrying was associated with greater brooding reduction (eight-predictor model: B=0.71, p=0.026) and remained significant in the single-predictor analysis (B=0.36, p=0.014). Self-criticism showed a negative association in the eight-predictor model (B=−0.60, p=0.043) but did not persist in the single-predictor analysis. In TAU, no personality trait was associated with brooding change. Adjusted between-group differences in change (brooding, GRID-HAMD17, total DDD) were not significant. Limitations: Nonrandomized allocation, modest sample sizes, and two assessment time points limit precision and power; the eight-predictor model in CBT may be prone to overfitting, so findings are exploratory. Conclusion: In this observational cohort, personality traits, with anxious worrying appearing relevant, were associated with brooding change within CBT, whereas between-group differences were not significant. These hypothesis-generating results require validation in adequately powered randomized trials to inform stratified depression care.