were carried out using PLINK. To evaluate potential population stratification effects, the UT and WI cohorts were analyzed for population admixture using STRUCTURE [71] on 94 non-related loci and an assumed population of 2. No significant admixture was observed, supporting the European American self report. Also, cohorts did not differ in CHRNA5-A3-B4 haplotype frequency (χ2 (6, N = 5654) = 8.2, P = 0.22, see Table 2), suggesting they were drawn from the same population.
