SNPs were tested for association with ADHD using logistic regression in PLINK assuming an additive model. The EIGENSTRAT software package was used to calculate principle components by inferring continuous variation in allele frequencies reflecting ancestral differences in individuals (25). Two principle components were identified and used to control for population stratification since they had the maximum impact on the genomic control inflation factor λ. Genome-wide significance was considered to be achieved when the p value reached 5×10–8 (26).
