One approach to predicting the outcome of future studies rests on the observation that most GWA meta-analyses are actually quite underpowered to discover the loci that reached genome-wide significance in those studies. In other words, given the variance explained of these loci when estimated in independent samples, the power to reach genome-wide significance was low, and the investigators were “lucky” to find the association. Besides the discovered loci, many more loci with similar effect sizes remained undiscovered. For example, if there are 20 variants that explain equal small amounts of phenotypic variance, then a study with 10% power for any one variant will identify 2 new associations on average, and miss the remaining 18. From these considerations of power, it is possible to extrapolate from current results to future studies, at least for variants that have an effect size (variance explained) that is at least as large as some of the variants discovered in the earlier study (54, 78, 99). These methods have been reasonably accurate in predicting future discovery of loci with similar effect sizes to those identified in
