Over the years, the U.S. Census Bureau has collected information on race and ethnicity. The census form has always reflected changes in society, and shifts have occurred in the way the Census Bureau classifies race and ethnicity. Historically, the changes have been influenced by social, political and economic factors including emancipation, immigration and civil rights. Today, the Census Bureau collects race and ethnic data according to U.S. Office of Management and Budget guidelines, and these data are based on self-identification.