Table 3 shows the power to filter out a SNP when its allele frequency in the second population ranges from 0.3 down to 0.05, assuming that there is no genetic effect (odds ratio of 1) in the second population. As expected, power is reduced as the minor allele frequency decreases: when the allele frequency p = 0.3, power to detect a significant population-by-genotype interaction at the α = 0.05 level is 61% compared to power of 25% when p = 0.05. Recruiting a larger sample of African Americans would allow us to further refine the region of association and make a more definitive conclusion about rs16969968. Nevertheless, with only approximately 61% power even when p = 0.3, in our data we have good evidence to be able to rule out SNPs such as rs9788721 and rs10519203 (Table 2). Note furthermore that rs8034191 is filtered out (heterogeneity p-value of 0.048) despite having a MAF of only 0.15 in the AA sample, corresponding to an estimated power between 34% and 52% at the α = 0.05 level.
