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 epi demiological samples. Can comorbidity be understood as meaningful covarianc e, and is this covariance structure linked with personality? We addressed t his question in a sample of 634 female and 549 male, middle-aged participan ts in the Minnesota Twin-Family Study (MTFS). Mental disorders were assesse d using the Structured Clinical Interview for DSM-III-R, the Substance Abus e Module from the Composite International Diagnostic Interview, and a speci ally-designed interview for the assessment of antisocial personality disord er. Personality was assessed using the Multidimensional Personality Questio nnaire. Relations among symptom scales for eight common DSM disorders were compatible with hypothesized underlying bivariate normal distributions. Pol ychoric correlations among these scales were well-fit by a two-factor model positing internalizing and externalizing factors, which, in turn, were cor related with broad personality dimensions. Internalizing was positively cor related with negative emotionality (and negatively with positive emotionali ty in women) and externalizing was negatively correlated with constraint. These findings suggest that internalization, externalization, and their lin ks to personality may provide a useful framework for understanding covarian ce among common adult mental disorders. (C) 2001 Elsevier Science Ltd. All rights reserved.