Chunk #90 — 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
Power is complex and depends on a variety of factors, including those in equation 1, but also on the true effect size, which is often not known until research is conducted. We evaluated how power would change under a variety of favorable circumstances (indeed, unrealistically favorable). In particular, we calculated power for the largest effect sizes reported for selected phenotypes in Figure 1 and then recalculated power assuming the investigator implemented a highly effective extreme sampling design and highly precise measures (see Table 3). First, we calculated the sample size required to have 80% power to detect the original reported effect. As can be seen from Table 3, sample sizes that are unheard of in electrophysiological research would be required. Under realistic circumstances, such as that reported by ENIGMA for hippocampal volume (Stein et al., 2012), 15,258 total samples would be required for 80% power to detect a single genome-wide effect. Next, we estimated the sample size required if one were to maximize the variance of X (VX) or to reduce measurement error from 50% to 25%. We assume that
