A potential further confounding factor is population stratification, which causes GWAS associations to tag population differences rather than disease associations.24 To resolve this issue, a homogeneous population is selected in which population outliers are excluded, and principal components are used to reduce overall genetic variation and thus capture and account for remaining stratification due to genetic ancestry.24 In this Rapid Review, we focus on GWAS done in populations of European ancestry due to their large sample sizes and increased statistical power, but GWAS have also been performed in other ethnicities (panel 3). Fine–scale population structure could still be an under lying issue that can be partly accounted for by covarying on more principal components.29 Fully accounting for population structure might require more complex models that adjust for local ancestry of specific regions of DNA to truly be controlled.24
