the legal and official designation of who is native american has aroused controversy by demographers, tribal nations, and government officials for many decades. federally recognized tribes and state recognized tribes set their own membership requirements; tribal enrollment may require residency on a reservation, documented lineal descent from recognized records, such as the dawes rolls, and other criteria. some tribes have adopted the use of blood quantum, requiring members to have a certain percentage. the federal government requires individuals to certify documented blood quantum of ancestry for certain federal programs, such as education benefits, available to members of recognized tribes. but census takers accept any respondent's identification. genetic scientists estimated that more than 15 million other americans, including african americans and hispanic americans (specifically those of mexican heritage), may have up to one quarter of american indian ancestry.