Future studies should examine the relationship between neuroticism and other forms of psychopathology, especially externalizing psychopathology. Several studies suggest relationships among externalizing psychopathology, internalizing psychopathology, and neuroticism. For example, Krueger and Markon (2006) found, in their meta-analysis, that internalizing psychopathology correlated .5 with externalizing psychopathology. In a study of child and adolescent twins, Lahey et al. (2008) found that major depressive disorder and generalized anxiety disorder were related strongly both to externalizing symptoms and to internalizing symptoms. Sher, Grekin, and Williams (2005) reviewed the literature and found that, in some studies, neuroticism appears to be an outcome of alcohol use, but other evidence suggests negative emotionality may precede problematic drinking. More research is needed, and the nature of the relationships among neuroticism, internalizing psychopathology, and externalizing psychopathology can be clarified in longitudinal studies.
