To avoid population stratification (Cardon & Palmer, 2003), we conducted our analyses separately by ancestry group. Genetic ancestry principal components were computed from GWAS data using Eigenstrat (Price et al., 2006) and the 1000 Genomes, Phase III reference panel. Individuals were assigned an ancestry classification (European, African, or Other) based on the first two principal components. Our analyses included participants of European (EA) and African (AA) ancestry.
