explaining 1% or less of the variation each. Visual inspection showed very little individual admixture within each self-identified ethnic group, indicating a small potential for confounding because of population stratification. In addition, we empirically tested the impact of population structure on the analysis by running the base model adjusted for coefficients of ancestry or principal components within the self-identified ethnic groups. The effect estimates obtained from the adjusted analysis were neither substantially different in comparison with the unadjusted analysis nor did the corresponding P-values change considerably. Thus, we did not adjust for the variability captured by the coefficients of ancestry or principal components within the self-reported ethnicity when analyzing the Caucasian-only sample. However, we limited the analyses to only the individuals who self-identified as Caucasian because of the potential for differential linkage disequilibrium across different ethnic groups leading to heterogeneity in effect estimates.
