Background: This study investigated the association between dimensional personality traits from the Five-Factor Model (FFM) and treatment outcome in patients with Major Depressive Disorder (MDD).
Methods: Six hundred forty-nine outpatients with MDD participated in a randomised double-blind longitudinal study for 6 months. Patients received a combination of medication and psychotherapy; they were randomised to medication condition (tianeptine or fluoxetine), and non-randomly assigned to psychotherapy condition (supportive, cognitive-behavioural, or psychodynamic). The Montgomery Asberg Depression Rating Scale was used to assess depression severity. The Système de Description en Cinq Dimensions was used to assess the personality domains of the FFM.
Results: Group comparisons revealed that patients who responded to both medication and psychotherapy had lower Neuroticism (t=4.22, p<.01), and higher Extraversion (t=4.01, p<.01) and Openness to Experience scores (t=3.57, p<.01) compared to non-responders. Regression analyses, which controlled for shared variance among the five personality domains, indicated that Neuroticism (chi(2)=4.06, p=.04) and Conscientiousness (chi(2)=8.98, p<.01) were significantly and uniquely associated with response. The two-way interactions between NeuroticismxExtraversion (chi(2)=4.49, p=.03) and ExtraversionxConscientiousness (chi(2)=5.91, p=.01) were also associated with response. These results were mostly replicated across the treatment-completer and intent-to-treat samples.
Conclusions: Dimensional personality traits predict response for individuals with MDD.
Limitations: This study did not examine facet-level traits, patient pre-morbid personality and functioning, and additional patient characteristics. Results may not be generalizable to severely depressed or treatment refractory patients.