pairs of affected and unaffected individuals, matched on two dimensions of genetic ancestry using the function pairmatch in the package optmatch in R (1-to-1 fullmatch) (Supplementary Materials). The sixth assessment of data was conducted as was done for the fifth, using only individuals of European ancestry. Pair matching, as done in the fifth and sixth assessments, is a common epidemiological approach for controlling confounding (here, differences in ancestry in cases versus controls) and has been shown to be useful for genetic studies (27–29). Note assessments 3–6 use all high-quality SNPs.
