Finally, we tested how the gene-by-intervention interaction effect manifested over the adolescent period. Fast Track intervention children who carried “A” alleles exhibited a slower progression of substance use behavior during adolescence as compared to “A” carriers in the control condition; children who did not carry an “A” allele exhibited similar patterns of change in substance use during adolescence (i.e., gene-by-intervention-by-time effects in repeated measures ANCOVA analysis for alcohol use, ηp2=0.012, p=0.014; for cannabis use, ηp2=0.017, p=0.010). Gene-by-intervention effects on delinquency did not change over the 8-year period (ηp2=0.007, p=0.178). Between-subjects ANCOVA analysis indicated statistically significant differences in mean levels of externalizing behaviors (for delinquency, ηp2=0.042, p=0.002; for alcohol use, ηp2=0.042, p=0.002; for cannabis use, ηp2=0.051, p=0.001). Complete model results are reported in Appendix Table A5xiii. Figure 4 shows average levels of each of the externalizing measures from grade 7 through two years post-high school in the intervention and control groups for carriers and non-carriers of the rs10482672 “A” allele.
