Despite the presence in our analyses of personality traits widely seen as good indices of the internalizing and externalizing dimensions of psychopathology, the hypothesis that these spectra might be best captured at the level of personality or temperament was not supported empirically (Krueger & Tackett, 2003; Clark, 2005). This is unfortunate because such scales are more informative about the broad range of vulnerability than a dichotomous diagnosis, and easier and cheaper to measure. For the externalizing dimension, these results might have differed if we had had other personality measures that more directly assessed disinhibition/impulsivity or meanness/callousness (Patrick et al. 2009). Our results are also consistent with a prior multivariate twin analysis in the sample showing that a substantial proportion of the genetic variation for internalizing disorders was not captured by N (Hettema et al. 2006).
