OR of 1.5 we need a sample size of 801 to obtain 80% power at a significance threshold of 0.05 [46]. For an OR of 1.2 (a more reasonable, but still conservative, estimate of effect size) the required sample size is 2,340, while for an OR of 1.1 it is 8,414. In fact, no study is adequately powered to detect an OR of 1.2, and only five would be able to reliably detect an OR of 1.5. The median sample size of all studies is less than 200, adequately powered only to detect an OR of 2.5 or above. In short, these studies on intermediate phenotypes are underpowered, and their results should be treated with extreme caution[23].
