Using the Genetic Power Calculator,34 we determined that our sample had 78% power at P=.05 with unscreened controls (risk allele frequency=0.3; disease prevalence=0.025; genotypic relative risk Aa=1.4 and AA=1.8; marker allele frequency=0.3 at D′=0.9 with risk variant). When we selected screened controls and used otherwise identical parameters, power rose only slightly, to 80%. We conclude from these calculations that our partially unscreened control sample did not significantly affect our study results.
