An approach commonly used to correct for PS is to adjust simultaneously for a fixed number of top- ranked PCs or for those PCs that have significantly large genetic variation according to the Tracy-Widom test [15], [16]. This approach might not be optimal if selected PCs are distributed almost equally in cases and controls [26]. In Text S1, we have presented an illustrative example of how unnecessary adjustment of population substructure (even one PC) could lead to a significant loss in power (Text S1, Table S1).
