In population-based samples, externalizing disorders assessed at personal interview—most typically conduct, antisocial personality, and drug and alcohol use disorders—have high rates of comorbidity and form, in multivariate analyses, a discrete psychopathologic dimension (Krueger et al. 1998, 1999, 2001). Twin studies from Virginia (Kendler et al. 2003), Minnesota (Hicks et al. 2004) and Norway (Kendler et al. 2011) have all suggested that these disorders share a common genetic liability that is largely responsible for their tendency to cluster together in human populations.
