Because of the requirement to adjust for the large number of statistical tests in order to control Type 1 error, adequate statistical power (to minimize Type 2 error) is crucial particularly given the small genetic effect sizes typical for human GWAS findings (see below). Figure 1 shows power curves for four different sample sizes. Given the large number of statistical tests and as the genetic effects are likely to be quite subtle, power is inadequate unless very large numbers of cases and controls are studied.
