2020 Census: Coverage Errors and Challenges Inform 2030 Plans
Fast Facts
Every 10 years, the Census Bureau counts the entire population of the United States. Decision-makers use this information to apportion congressional seats and direct federal funds.
The last census, in 2020, occurred during COVID-19, which disrupted the Bureau's efforts—risking the quality and accuracy of the count.
We reported accuracy issues with the census, including that the Bureau estimated 14 states had significant errors in their population counts. We found that long-standing challenges with the census may have contributed to accuracy issues with the 2020 count. For example, young children and minorities continued to be hard to count.
Highlights
What GAO Found
The U.S. Census Bureau's 2020 Post-Enumeration Survey estimated that two geographic regions and 14 states had statistically significant net coverage errors in the 2020 Census. Net coverage error is the difference between the census count and the survey estimate of the actual population size. The survey results also showed that under- and overcounts persisted for various demographic groups. For example, in 2020 and 2010, Black or African American and Hispanic persons, young children, and renters were undercounted, while non-Hispanic White persons, adults over 50, and homeowners were overcounted. However, the survey estimated no statistically significant net coverage error for the national population count. The Bureau reported that this estimate was consistent with the survey's national estimate in 2010.
Historical Under- and Overcounts Persisted for Some Race and Ethnic Groups in the 2020 Census
Note: For more details, see figure 5 in GAO-25-107160.
The COVID-19 pandemic and other long-standing challenges potentially affected the accuracy of 2020 Census counts. GAO previously reported on these challenges, including the Bureau's late census design changes, staffing issues, and budgetary uncertainty. GAO and others have reported that errors in census data may result in potential implications for uses, including allocating funds.
As of October 2024, the Bureau had plans for over 50 research projects and other efforts to inform the design of the 2030 Census. GAO identified examples of projects and related efforts that leverage insights from 2020 Census coverage challenges to improve accuracy in the 2030 Census across four categories: (1) public engagement, (2) use of data collected by governments while administering programs, (3) Post-Enumeration Survey design, and (4) operations. For example, the Bureau has planned projects to improve data collection to address challenges with counting people in group quarters like prisons and college dormitories.
Why GAO Did This Study
The Bureau assesses the accuracy of its census counts with an independent process—the Post-Enumeration Survey. Results from this survey showed that some states and demographic groups (i.e., populations by characteristics such as race and age) were under- or overcounted in 2020. GAO has previously reported on the long-standing problem of coverage errors for various population groups.
GAO was asked to report on the Bureau's efforts to assess accuracy of the 2020 Census. This report describes (1) Bureau assessments of the 2020 Census population counts and how they compare to previous censuses; (2) potential causes and implications of coverage errors in the 2020 Census; and (3) steps the Bureau and census stakeholders identified to improve the accuracy of the 2030 Census.
GAO reviewed the Bureau's Post-Enumeration Survey measures for the 2020, 2010, and 2000 censuses. GAO also reviewed Bureau and other authoritative sources' reporting on the accuracy of the 2020 Census and its challenges and potential changes to improve the accuracy of the 2030 Census. GAO also interviewed Bureau officials.
GAO provided a draft of this report to the Department of Commerce for its review. The Bureau provided technical comments, which GAO incorporated, as appropriate.
For more information, contact Yvonne D. Jones at (202) 512-6806 or jonesy@gao.gov.