Chunk #85 — 7.0 Recommendations to Advance Endophenotype Genetics — 7.3 Adequate power to detect individual effects is crucial but almost never attained in existing endophenotype genetic association studies — 7.3.1. Power and sampling schemes in GWAS
terms in the denominator (or halving MSE) will have exactly the same effect as doubling n. Thus, doubling the variance in X will have exactly the same influence on power as doubling the sample size. When X is the genetic variant increasing its variance is achieved by increasing its minor allele frequency – through sampling individuals from the phenotypic or genetic extremes (from diverse ancestries, for example). Doubling the variance in the predictor not shared with other predictors, by choosing independent covariate sets, for example, will have the same effect. Finally, we see the importance of phenotypic measurement, as more precise measures with less error will decrease MSE and thereby increase power. Although electrophysiological endophenotypes are often measured reliably compared to, for example, fMRI measures, error can be reduced through aggregating multiple measurements (Ford, 2014).
