A series of three models predicting 9th-Grade Alcohol Use were conducted to examine Hypotheses 2 through 4. The first model included main effects of OXTR risk, Intervention Status, and Peer Substance Use; the second model added the three two-way interactions; and the last model included the three-way interaction with the subordinate two-ways and main effects retained (see Table 2 for full results). Results supported Hypothesis 2: While controlling for Intervention Status and OXTR risk, higher peer substance use was related to higher adolescent alcohol use (b = 0.82, p < .01). Main effects of intervention status (b = 0.03, ns) and OXTR (b = −0.01, ns) on alcohol use were not significant, however. None of the two-way interactions were significant when added to the model, demonstrating no support for Hypothesis 3. OXTR variation did not moderate the impact of affiliations with substance-using friends on adolescents’ own alcohol use. However, the significant three-way interaction in the final model supported Hypothesis 4 (b = -0.22, p < .05). OXTR variation did moderate the impact of intervention status on links between affiliations with substance-using friends and individual adolescents’ own alcohol use. Parameters in this last model were robust to the PC1 covariate.
