Study subjects
We downloaded the SNPs data from Haplotype Map (HapMap) phase 3 (http://www.hapmap.org) for CEU (Utah residents with Northern and Western European ancestry), JPT (Japanese in Tokyo, Japan), and YRI (Yoruba in Ibadan, Nigeria). We focused on the gene-based SNP associations in the three ethnicities, because ethnicity is a highly heritable polygenic quantitative trait of biomedical importance. Ethnicity-specific SNPs were obtained by eliminating common SNPs.