All COGA DNA samples were genotyped for a 96 SNP (single nucleotide polymorphism) array (Fluidigm SNPtrace, Rutgers University Cell and DNA Repository) that included 64 ancestry informative markers. The principal components derived from these SNPs were used to assign ancestry, and were the basis for the selection of the European Ancestry (EA) families. Prioritization of families was based on the most informative families, defined as those with the largest number of alcohol dependent family members with DNA and electrophysiological measurements. The analytic sample consisted of all family members with both resting state EEG and GWAS data available: 1,564 individuals (824 females and 740 males; average age: 31.6) from 117 multi-generational families affected with AD. Family sizes ranged from 4 to 39 individuals with an average of 13.4 individuals (with EEG data) per family.
