Turning to the third aim of this study, we found very similar and substantial genetic correlations between the externalizing and internalizing genetic common factors in men and women. These correlationswere higher than observed between the Axis I and Axis II internalizing and externalizing genetic factors identified in a recent multivariate analysis of a Norwegian cohort (Kendler et al. 2011) (estimated at +0.16 and +0.36 respectively). However, the correlations we observed were broadly consistent with phenotypic correlations between internalizing and externalizing common factors observed in the USA (+0.51) (Krueger, 1999), New Zealand (+0.45) (Krueger et al. 1998) and The Netherlands (+0.56) (Vollebergh et al. 2001).
