In the 1930s, the Department of Interior conducted physical examinations of 209 individuals residing in Robeson County and determined that 22 possessed at least 1/2 or more degree of Indian blood, and that 18 more were borderline or near-borderline cases. Scholars and scientists no longer consider such physical exams to be a valid method of determining biological ancestry. Each federally recognized tribe has the authority to determine membership criteria and establish its own rules. These are generally based on documented descent from a historical list of agreed-upon members or descent from known living members.