the significance of the age-varying G x I interaction effect (β3) by exponentiating the Poisson coefficient to yield an IRR effect size and comparing this estimate to a value of 1 (corresponding to a Poisson β=0). The G x I interaction effect was declared significant at ages where the 95% confidence interval of its IRR effect size did not overlap with 1. Second, we unpacked the interaction by generating genotype-specific intervention slopes describing the age-varying intervention effect for each GABRA2 genotype (separately for A carriers and TT youth) from the model estimates. Third, we generated group-specific intercept functions that described estimated alcohol misuse levels as a function of age for each GABRA2 genotype by intervention condition subgroup.
