Because population genetic admixture may confound G×E findings (Halder et al., 2009), we used the Structure program, version 2.3.4 (Falush, Stephens, & Pritchard, 2007) with a panel of 24 ancestry informative markers to estimate an ancestry proportion for each participant. Three ancestral populations (African, European, and Other) were found to be relevant to characterizing ancestry, and so racial admixture variables (Ancestry proportion 1, Ancestry proportion 2) were used as covariates in the analyses. Average level of European Ancestry was 28.9%
