To characterize ethnic heterogeneity in our sample, principal components were estimated based on the SAGE genome-wide data, using the procedure described by Price and colleagues (2006). Two major principal components emerged, corresponding to European vs. African ancestry (PC1) and Hispanic vs. non-Hispanic ancestry (PC2). Treating ancestry as a covariate assumes that while minor (i.e. less common) allele frequencies may differ between races, the biological impact of SNPs does not (Ioannidis, Ntzani, & Trikalinos, 2004). While ideally we would model ethnicities separately to explore this, our sample size prevented this approach. PC1 and PC2 were used as covariates in our analyses, along with age (coded in quartiles as three dummy codes, as has been done in previous SAGE analyses, corresponding to ≤34, 35–39, and 40–44, with 45+ as the reference group), and sex (1 for males and 2 for females). SNPs were coded as 0/1/2 to indicate the number of minor alleles present for a given individual. We did not control for alcohol dependence case status for our main analyses, because sensation seeking is substantially related to alcohol use behaviors (Zuckerman,
