An additional 380 unlinked SNPs were genotyped for STRUCTURE [16] analysis to allow tests for the absence of confounding population structure. Using a two cluster solution computed in duplicate, no significant association between estimated cluster membership probability (inferred ancestries) and case-control status was found after accounting for self-reported race/ethnicity. Furthermore, these probabilities are perfect predictors of self-reported race. The same lack of association holds for three, four and five cluster solutions. These results indicate that our logistic regression framework described below, which analyzes the full sample while accounting for race as a covariate, is appropriate.
