in PCA space (Conomos et al., 2018; Heckerman et al., 2016; Zhang and Pan, 2015). For example, race and ethnicity are often correlated with socio-economic status and other environmental risk factors for disease. Self-reported ethnicity or other variables that capture trait heterogeneity on the basis of socio-cultural factors may also be appropriate to consider as covariates in those instances (Banda et al., 2015; Medina-Gomez et al., 2015). Directly controlling for local ancestry tracts in variant-level association analyses may further improve power and reduce false positives in admixed samples (Li & Keating 2014).
