The software package EIGENSTRAT/EIGENSOFT34 was used to calculate principal components reflecting continuous variation in allele frequencies representing ancestral differences in subjects. A description of the principal components extraction process may be found in related publications.27,33 Briefly, two principal components, the first distinguishing African-American participants from European-American participants and the second distinguishing Hispanic and non-Hispanic subjects, were identified and used to control for effects of population stratification. The self-reported ethnicity of the sample analyzed in this study is 2698 European Americans, 1257 African Americans and 8 individuals of other ethnicity.
