First, consistent with prior studies based on personal interviews (Hicks et al. 2004; Kendler et al. 2003, 2011), we found substantial sharing of both genetic and environmental risk factors across the three externalizing syndromes of DA, CB and AUD. Because the syndromes in our sample were ascertained from registries, our results rule out the possibility that prior evidence for an externalizing spectrum is an artifact of measurement due, for example, to rater or reporter bias.
