The statistical power in testing gene-environmental interaction is a function of sample size, prevalence and relative risk of risk genotype, prevalence and relative risk of environmental factors, type I error, and hypothesized G*E interaction relative risk. The power of our study sample (N=2027) to detect a gene-environment interaction relative risk of 2.50 or higher between SNP rs16969968 (risk genotype frequency 12.5%) and low parent monitoring (prevalence 22.9%) is estimated to be 0.70 at α=0.05. We found a significant interaction between rs16969968 and parent monitoring. Our study sample has the sufficient power greater than 0.80 to detect a gene-environment interaction relative risk of 1.85 or higher between SNP rs3743078 (protective genotype frequency 40.2%) and low parent monitoring (prevalence 22.9%) at α=0.05. However, we found no significant interactions between rs3743078 and parent monitoring.
