The foregoing considerations lead to three specific hypotheses. First, we predicted that the intervention would yield similar outcomes for intervention-targeted parenting behavior regardless of youth genotype at DRD4 and that the SAAF program would work to alter intervention-targeted parenting behavior regardless of youth genotype. Second, we predicted that youths with one or two copies of the 7-repeat allele of DRD4 who were assigned randomly to the control condition would show greater increases in substance use over time than would youths with the same genotype who were assigned randomly to SAAF; this would not be true for youths with two copies of the 4-repeat allele. We further hypothesized that the differences would be due to differences in youth genotypes, not parental genotypes. In addition, we examined the exploratory hypothesis that parents with the DRD4 7-repeat allele might show less change in intervention-targeted parenting as a function of SAAF participation. Although this is not directly relevant to the differential susceptibility hypothesis, it is relevant to the broader issue of optimal construction of preventive intervention programs. The availability of parent genotypes provided an
