To avoid population stratification (Cardon & Palmer, 2003), we conducted our analyses separately by ancestry group. Genetic ancestry principal components were computed from genetic variants using Eigenstrat (Price et al., 2006). These principal components reflect continuous variation in allele frequencies, which represent ancestral differences. Individuals were assigned an ancestry classification (European, African, or Other) based on the first two principal components (Lai et al., 2019). Our analyses included participants of European (EA) and African (AA) ancestry, the two largest groups in COGA.
