University of Kansas sociologist Joane Nagel traces the tripling in the number of Americans reporting American Indian as their race in the U.S. Census from 1960 to 1990 (from 523,591 to 1,878,285) to federal Indian policy, American ethnic politics, and American Indian political activism. Much of the population "growth" was due to "ethnic switching", where people who previously marked one group, later mark another. This is made possible by our increasing stress on ethnicity as a social construct. In addition, since 2000 self-identification in US censuses has allowed individuals to check multiple ethnic categories, which is a factor in the increased American Indian population since the 1990 census. Yet, self-identification is problematic on many levels. It is sometimes said, in fun, that the largest tribe in the United States may be the "Wantabes".