Identification of the ancestry of an individual is dependent upon knowledge of the frequency and distribution of phenotypic traits in a population. This does not necessitate the use of a racial classification scheme based on unrelated traits, although the race concept is widely used in medical and legal contexts in the United States. Some studies have reported that races can be identified with a high degree of accuracy using certain methods, such as that developed by Giles and Elliot. However, this method sometimes fails to be replicated in other times and places; for instance, when the method was re-tested to identify Native Americans, the average rate of accuracy dropped from 85% to 33%. Prior information about the individual (e.g. Census data) is also important in allowing the accurate identification of the individual's "race".