The higher-order structure of common DSM mental disorders: internalization, externalization, and their connections to personality

Comorbidity among mental disorders is commonly observed in clinical and epidemiological samples. Can comorbidity be understood as meaningful covariance, and is this covariance structure linked with personality? We addressed this question in a sample of 634 female and 549 male, middle-aged participants in the Minnesota Twin-Family Study (MTFS). Mental disorders were assessed using the Structured Clinical Interview for DSM-III-R, the Substance Abuse Module from the Composite International Diagnostic Interview, and a specially-designed interview for the assessment of antisocial personality disorder. Personality was assessed using the Multidimensional Personality Questionnaire. Relations among symptom scales for eight common DSM disorders were compatible with hypothesized underlying bivariate normal distributions. Polychoric correlations among these scales were well-fit by a two-factor model positing internalizing and externalizing factors, which, in turn, were correlated with broad personality dimensions. Internalizing was positively correlated with negative emotionality (and negatively with positive emotionality in women) and externalizing was negatively correlated with constraint. These findings suggest that internalization, externalization, and their links to personality may provide a useful framework for understanding covariance among common adult mental disorders.