this distinction is muted when the HGDP sample is not included in the base calculations (b). In essence, the eigenspace aims to separate clusters like those included in the base. As a result, when using HGDP as a base, the axes do not highlight the differences in the POPRES sample causing them to clump together in the center of the eigenspace (a). Likewise, when using a POPRES base, the axes do not capture the strong differences in the HGDP data (b). Using data from both repositories produces an eigenspace that better reflects the full range of variability in the data (c, d). Using a balanced sample from the available data improves the separation between these populations (d).
