Since a given region still contains some degree of genetic variation, it’s possible for a reference group to miss some of that diversity. To use an analogy, if you selected 23 New Yorkers that all happened to all live in Little Guyana and made them a reference group for all New Yorkers, you might not get a representative sample of the city. Haplotypes common amongst Guyanese people would probably be overrepresented.
Jeff says that anything more granular than continent-level estimates involves some big-time guesswork. “We’re making a huge assumption that this variant is the only variant, and that these populations are somewhat of a monolith,” she says. “We really do need more information to dig down to more detailed population differences within these continents.”
If Ancestry doesn’t have a reference population that matches your specific ancestry, the algorithm will assign you the next closest region. There’s no reference group for