Researchers use two main measures to determine who was missed in the 2010 Decennial Census: omissions and net undercounts. Omissions reflect the number of people who should have been counted in the census but were not, while net undercounts reflect the percent of people who were missed minus the percent who were double counted.
Census omissions and net undercount rates both reflect dimensions of census accuracy, but they often tell different stories. Analysis shows a nationwide omissions rate of 5.3 percent compared to a net undercount rate of 0.01 percent. This paper focuses on census omissions. In the 2010 U.S. Census, there were nearly 16 million omissions.
Omissions rates vary among demographic groups in much the same pattern as seen in net undercount rates. Racial and Hispanic minorities have higher omissions rates than non-Hispanic whites. Renters (8.5 percent omissions rate) are more likely than homeowners (3.7 percent) to be omitted in the census. Among the states, omissions rates range from a low of 2.6 percent in Iowa to a high of 8.9 percent in Mississippi. Large cities tend to have higher omissions rates than the rest of the country.
Obtaining an accurate count of state and local populations is important because the data affect the balance of political power across geographic areas and are widely used for state and local decisionmaking. For example:
- Seats in the U.S. House of Representatives are apportioned based on decennial census data.
- More than $850 billion in federal aid was distributed in FY 2016 based on state and local census data.
- Planners use local census data to decide where to build new roads, schools, and hospitals.
- Businesses use census data to inform their location or relocation decisions.
A comprehensive picture of census accuracy requires assessment of the number, characteristics, and geographic locations of those who are missed in the census in addition to analysis of net undercount rates. By understanding who was omitted in the 2010 Census, community leaders, advocates, and others can better target geographic areas and population subgroups for get-out-the-count efforts to reduce the number of people who are missed in the 2020 Census and improve the accuracy of the count for state and local populations.
I would like to acknowledge support from the 2020 Census Project, a funders collaborative to promote a fair and accurate census, hosted by New Venture Fund. I would also like to thank Linda A. Jacobsen and Mark Mather at Population Reference Bureau (PRB) for reviewing and providing comments on this report, and Paola Scommegna and Lillian Kilduff at PRB for their editorial assistance.