In this study, we aimed to extend the present knowledge regarding the relationship of personality traits, as specified by the five-factor model (FFM), with the affective morbidity of bipolar I disorder. The primary aim of this study is to investigate the association of personality traits with affective morbidity, particularly with hospitalization for depressive, manic, or mixed episodes, in patients with bipolar I disorder. The Revised NEO Personality Inventory was administered to 83 subjects who showed a euthymic mood state. Multivariate Poisson regression analysis was performed to identify associations between five domains of personality and the number of hospitalizations for affective episode(s) (manic, depressive, and mixed state). As a secondary research interest, we attempted to determine personality traits which would be significantly different between subjects with Affective Switch from mania into depression Without Euthymia (ASWE) and non-ASWE. The Neuroticism score was positively associated with the number of hospitalization for depression and the total number of hospitalizations Extraversion and Openness scores showed a negative relationship with the number of hospitalizations for depression and the total number of hospitalizations. We found that ASWE patients showed significantly higher Neuroticism scores than did the non-ASWE group. However, there was no significant association between the hospitalization for manic episode and any particular personality trait based on the FFM. This study reveals that personality traits based on the FFM may contribute to an increased likelihood of depressive morbidity and switch into depression.
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