exposure-based interpretation for ORge, specifically ORE | G=1 / ORE | G=0. Table II shows the required number of case-control pairs required to achieve 80% power for detecting an interaction, for various underlying values of ORge, minor allele frequencies, and exposure prevalences. The range of exposure prevalences represents that of many common environmental exposures, including physical inactivity, obesity, and smoking. An exposure prevalence of 0.1 is representative of physical inactivity in non-Hispanic whites (10.9% according to Centers for Disease Control (CDC) statistics for 2007) and that of 0.5 is representative of obesity in non-Hispanic black women (53% according to National Health and Nutrition Examination Survey (NHANES) statistics from 2003–2006). The prevalence of physical inactivity in other racial/ethnic groups, obesity in other racial/ethnic/sex groups, and smoking (19.8% according to CDC statistics for 2007) falls between 0.1 and 0.5. The required sample size to detect a significant G×E interaction of reasonable magnitude in a GWAS at p<10−7 is approximately two to three times larger than that needed to test a single variant at p<0.05 due to the correction for multiple testing.
