of SAAF and genotype in the second step of the regression. As can be seen in Table 2, model 1a, the main effects for SAAF and genotype were nonsignificant. However, in model 1b, the interaction of SAAF participation with the presence of the “s” allele was significant. Figure 2A depicts the interaction effect. As can be seen, s allele carriers showed, on average, a greater response to SAAF. There were significant differences in early substance use initiation between those with differing genotype only for those in the control group. Those in the treatment condition did not show significant differences in substance use initiation related to genotype, replicating prior analyses with the full sample (Brody, et al., 2009).
