cannabis as illicit drug use. Since more than half the sample are characterized as regular users of cannabis at some time during the age range of the study (46% among those from community sample), regular use of cannabis can not be considered a practice that violates norms of age-related behavior or involves enhanced risk taking, and thus not an element of “externalizing psychopathology”. We note that 90% of cannabis dependent subjects who are also alcohol dependent are included in the subsample, so although our criterion does not span regular cannabis use we are probably picking up those more genetically vulnerable cannabis dependent subjects and thus paralleling the group used in Dick et al. (2007). For the regular alcohol use outcome, there were a sufficient number of illicit drug non-users who became regular users of alcohol to provide a subsample to contrast with the illicit drug use subsample. Since about 75% of the alcohol dependent subjects were members of the illicit drug use subsample, there were too few alcohol dependent subjects with no illicit drug use to provide a contrasting subsample. However some inferences about the significance of illicit drug use for the onset of alcohol dependence can be drawn from
