Table 1 presents predictors of residualized increases in substance use across the 22 months separating the pretest and long-term follow-up assessments. Model 1 in Table 1 showed a significant DRD4 effect on youths’ substance use. Youths who carried at least one l allele of DRD4 showed a 53% increase [100*(1-e.425)] in frequency of substance use compared with youths carrying two s alleles. In the presence of DRD4 status, neither intervention effects nor gender effects were detected. Model 2 in Table 1 presents tests of hypothesized interaction effects. The hypothesized three-way interaction among DRD4 status, intervention status, and youth gender was significant (β = −1.398, p = .023), indicating that a significant difference emerged in the DRD4 status × intervention effect on increases in substance use for youths of one gender only. This finding was explored further via separate tests of 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
