risk. Consistent with P300 amplitude being associated with risk for an externalizing dimension underlying vulnerability for substance use disorders (Hicks et al., 2007; Patrick et al., 2006) and findings that paternal AAB is a more severe indicator of externalizing than of alcohol dependence (Krueger et al., 2005), our hypothesis would predict the greatest difference between the sons of fathers with AAB and a low-risk group. This was the case. Men with a paternal history of alcohol dependence but no AAB or drug dependence would be predicted as being intermediate between the low-risk group and the paternal AAB group. Although there was a trend for a difference in trajectory between this intermediate paternal externalizing risk group and the paternal AAB group, this was not statistically significant by conventional standards. This intermediate-risk group also did not differ significantly from the low-risk group. The ability to detect externalizing risk group differences may require a fairly large difference in the level of paternal externalizing severity.
