shows, SAAF reduced growth in past-month substance use only for youths with one or two copies of the 7-repeat allele for DRD4. The effect size of 0.26 for the interaction of genotype with intervention accounted for 2% of the explained variance in outcomes. Within-group analyses indicated a significant protective effect of SAAF only for those with the 7-repeat allele of DRD4 (γSAAF = -.69, p < 0.01). For those with the 4-repeat allele, the effect was in the opposite direction (γSAAF = .33, p < 0.01).
