First, for each SNP, we checked whether genotype correlated (p > .01) with demographic measures including gender, BMI, education in years, age, current and lifetime substance use. We also evaluated whether any of the demographic factors correlated with stop RT or go RT. If they did, we included them as covariates in further analyses. If the minimum allele frequency was <0.1 we combined the rare homozygous genotype with the heterozygous genotype.
