Because neuroticism is linked to increased risk for many different mental disorders, it not surprising that it also is related to greater comorbidity among those mental disorders (Khan et al., 2005; Middeldorp et al., 2006; Weinstock, 2006). Indeed, in one large study, variations in neuroticism explained 20–45% of the comorbidity among depression and anxiety disorders and 19–88% of the comorbidity of those disorders with alcohol dependence and drug dependence (Khan et al., 2005). This is important because persons with comorbid mental disorders have more persistent and disabling disorders, and are more likely to use high-cost mental health services, than persons who meet criteria for only one mental disorder (Kessler, Chiu, Demler, & Walters, 2005). Furthermore, higher neuroticism is associated with greater use of mental health services even when the number of comorbid mental disorders is controlled (Jylha & Isometsa, 2006; ten Have, Oldehinkel, Vollebergh, & Ormel, 2005). In addition, persons with comorbid mental disorders have significantly poorer physical health and are more likely to be high-end users of medical services (Rush et al., 2005). This means that neuroticism is centrally
