The lack of genome-wide significant results suggests that common variants have at most a modest influence on smoking behavior. We had adequate power to detect a variant that explained even 2.5% of the variation in cigarettes per day. We had 61% power in the NHS sample and 71% power in the PLCO sample to detect such a variant at the 10−7 level; the power of the combined analysis was greater than 99%. Conversely, the lack of genome-wide significant findings does not rule out the existence of (many) common variants with small individual effects on smoking behavior, since our power to detect any one is small. Even with our relatively large sample size, our power to detect a variant similar to the 15q25.1 SNP rs1051730 (which was estimated to explain about 0.7% of the trait variance [44] at the genome-wide significance level) was only 8.5% for the combined analysis (and less than 1% for either study alone).
