DTSA results were calculated for the entire sample. Our fourth item for investigation, whether the influence of these SNPs would be greater in a behaviorally defined subsample comprising a putatively more genetically vulnerable group was suggested by the results of Dick et al. (2007) and King and Chassin (2007). Given the prevalence of various substance abuse categories in the sample and the number of subjects in each category who become alcohol dependent during the age range of the study, the broad criterion of the use of an illicit drug (see section 2.2) regardless of age of onset or frequency of use was employed to define the more genetically vulnerable group. This subsample will be called the “illicit drug use” subsample. Unlike the definition of illicit drug use in Dick et al. (2007), this definition does not categorize regular use of 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
