Another strength of the current study was the genotyping of 233 ancestry informative SNPs to assess intercontinental admixture within individuals of the same self-identified ethnicity (47–49). These SNPs were genotyped on individuals from multiple ethnic groups and analyses investigating the structure used the frequency of SNPs within each self-identified group to more accurately defined ancestry proportions for any given individual. These ancestry estimates were not only used to visually inspect the levels of admixture within Caucasians, but also to empirically compare unadjusted estimates to those adjusted by ancestry proportions. Although we demonstrated that the structure did not impact the analyses, we limited our final analyses to only Caucasians, as LD patterns can vary substantially across ethnic groups and may lead to heterogeneity in effect estimates, thus negatively impacting power despite the inclusion of additional samples.
