the DRD4 status × intervention status interaction for male and female youths. The results are presented in Table 2. Model 1 in Table 2 for male youths and female youths presents the main effect model. DRD4 status predicted an increase in substance use for male, but not female, youths. For male youths, carrying at least one l allele of DRD4 was associated with a 90% increase [100*(1-e.642)] in frequency of substance use compared with youths carrying two s alleles. Model 2 for male and female youths estimated the interaction effects for DRD4 status and intervention status. As hypothesized, this interaction was significant only for male youths; Figure 1 illustrates the interaction effect. Male youths carrying at least one l allele of DRD4 who were assigned randomly to the control program evinced larger increases in substance use than did their counterparts who were assigned randomly to the SAAF–T program or young men assigned to either condition who carried two s alleles. The next section deals with the results of tests of the mediated moderation hypothesis with male youths.
