Chunk #100 — 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 — 7.3.2 Power in GREML
For the sake of simplicity, power estimates for genetic correlations assume that the heritability of both traits is the same, using the same range of true heritability values as in panel A. Power is plotted for phenotypic correlations between the traits ranging from .10 to .40, and we assume that the genetic correlation between traits accounts for 80% of the phenotypic correlation. A sample of 10,000 is not nearly large enough to detect a genetic correlation of .08 (phenotypic correlation of .10), even if both traits are highly heritable (h2 = .60). If the heritability of the traits is relatively small in magnitude (h2 = .20), then nearly 10,000 subjects are required to detect the largest genetic correlation. If trait heritability is high and the phenotypic correlations are large, obviously an optimistic scenario, more than 3,000 subjects are still required. Factors such as the proportion of the phenotypic correlation accounted for by the genetic correlation and the degree to which the heritability of the two traits is similar affect power both positively and negatively, but the need for large samples is clear. When sufficiently powered, GREML analyses have the potential to provide insight into the genetic architecture of endophenotypes and
