Figure 3 shows the age-varying G x I interaction in a different way: by showing the estimated age-varying alcohol misuse means by intervention condition, presented separately by GABRA2 genotype. The left panel shows predicted age-varying alcohol misuse means for TT genotype adolescents in the control versus intervention conditions. For both intervention and control TT adolescents, alcohol misuse increased with age. However, estimates for intervention and control TT adolescents do not overlap between ages 13 and 16, suggesting that the intervention reduced alcohol misuse for TT youth most strongly during these ages. The right panel shows age-varying alcohol misuse estimates by control versus intervention conditions for youth with GABRA2 A genotypes, and shows that the developmental course does not differ between control and intervention A carriers, indicating no intervention effect for these youth. Additional comparisons (not shown in Figure 3) revealed that among control adolescents, TT genotype youth showed significantly higher levels of alcohol misuse than A carriers from ages 11.5 to 18. In contrast, among intervention adolescents, TT genotype youth showed lower levels of alcohol use compared to A allele carriers from ages 13–16.
