HapMap trios matched by ancestry to POPRES controls. The 30 offsprings from the HapMap, CEU sample, trios serve as cases and the 2184 individuals of European ancestry from the POPRES data serve as controls. (a) The plot displays the top two principal components of ancestry for cases (red) and controls (black) obtained using SGA. Based on the distribution of points in the eigenmap, many available controls would not be good matches to the HapMap trios. Only those delineated in blue are considered further. Each case is matched to one or more controls that are genetically similar based on the eigenvectors. (b) Distance between controls and closest case when matching in a random subset drawn from the full sample of controls versus (c) the distances when the controls consist of the restricted sample delineated in blue.
