Chunk #86 — 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
All these ways of increasing power should be considered to the extent possible in any study but, all else being fairly equal, the importance of sample size in genetic association studies cannot be overstated. Increasing sample size instead of increasing the variance of the predictor can be especially important in large-scale genetic association studies. In particular, extreme phenotypic sampling schemes to increase the variance of an associated genetic variant X (VX) are highly restrictive if one wants to evaluate a new phenotype. The original phenotypic sampling scheme to increase VX is not likely to increase the variance of other genetic variants associated with the new phenotype unless the correlation between the original phenotype, on which the sample selection was based, and the new phenotype is large. However, if the two phenotypes are highly correlated then sophisticated statistical procedures are required to help ensure that any genetic variant associated with the new phenotype is not spurious due to its confounding with the original phenotype (Liu & Leal, 2012).
