The Census Bureau’s release of the Modified Age & Race Census Files (MARC) on March 6, 2025, allows us to finally calculate 2020 Census coverage rates for young Black children (U.S. Census Bureau, 2025).
The MARC file is produced because the race categories used in the Demographic Analysis (DA) estimates the Census Bureau uses to measure accuracy of the Census, are not the same as the categories used in the 2020 Decennial Census. Those two sources should not be used to estimate the coverage of young Black children. The MARC files contain data using race categories consistent with those used in the DA estimates.
The Census Bureau (2025, page 1) describes the Modified Age & Race Census file as “The 2020 Modified Age & Race Census (MARC) files provide data from the 2020 Census in race categories that are consistent with the race categories used by the Population Estimates Program (PEP). Additionally, the age values for a subset of observations on the MARC files have been adjusted to produce more accurate age distributions.”
Census data show that historically young children, particularly Black and Hispanic young children, have had very high net undercounts in the U.S. Census (O’Hare 2014a; O’Hare 2014b; O’Hare 2015; Quiros and O’Hare 2023). In the 2010 Census the net undercount for young Black Alone children was 4.4 percent and for Black Alone or in Combination children it was 6.3 percent (O’Hare 2014b, Table 4). (Black Alone are children for whom only Black or African American race category was selected; Black Alone or in Combination are children for whom Black or African American race category was selected along with at least one other race category).
Other analysis shows that the census coverage of the Black population worsened between 2010 and 2020 (National Academy of Sciences 2023).
Results
Table 1 shows the 2020 Census coverage rates for Black children ages 0 to 4 derived by comparing the Demographic Analysis (DA) estimates to the results of the Modified Age & Race Census File. DA numbers are based on the birth, deaths, and net migration that occurred in the five years prior to the 2020 Census. Since births and deaths data are deemed complete and very accurate, the DA figures are thought to provide a true figure for the number of young children.
Results are shown for young children in the “Black Alone” category as well as those in the “Black Alone or in Combination.” The Black Alone or in Combination category is the most inclusive way to identify this racial group.
The 2020 DA estimate shows the number of young children in the Black Alone category is 3,043,000. The 2020 MARC file shows the number of Black Alone children ages 0 to 4 is 2,853,000. This means there was a net undercount of 190,000 young Black Alone children in the 2020 Census, and a net undercount rate for young Black Alone children of 6.2 percent.
The 2020 DA results show that the number of Black Alone or in Combination children ages 0 to 4 is 3,950,000. The 2020 MARC file shows the number of young children in the Black Alone or in Combination category is 3,667,000. This means there was a net undercount of 283,000 young Black Alone or in Combination children in the 2020 Census and a net undercount for young Black Alone or in Combination children of 7.2 percent. To provide a point of comparison, the coverage rate for the total population in the 2020 Census was -0.2 percent (U.S. Census Bureau 2022).
The Figure below shows how the coverage rates for young Black children from the 2020 Census compares to similar data from earlier censuses. The Figure shows the net undercount of young Black children has been relatively high since 1940, but the coverage of young Black children generally improved between 1980 and 2010.***
The coverage rate for the Black Alone category worsened from 4.4 percent in 2010 to 6.2 percent in 2020. The Black Alone or In Combination category worsened from 6.3 percent in 2010 to 7.2 percent in 2020. For both groups, the net undercount for young children is more than twice that of the overall Black population.
Summary
This analysis shows young Black children experienced a very high net undercount rate in the 2020 Census. While the overall U.S. population experienced a very small undercount (0.2 percent) the net undercount rate for the Black Alone population ages 0 to 4 was 6.2 percent and the net undercount rate for the Black Alone or in Combination population ages 0 to 4 was 7.2 percent.
These results indicate getting an accurate count of young Black children in the 2030 Census should be a high priority.
References
National Academy of Sciences (2023). Assessing the 2020 Census: Final Report, National Academy Press, https://nap.nationalacademies.org/catalog/27150/assessing-the-2020-census-final-report
O’Hare, W.P. (2014a). “Assessing Net Coverage Error for Young Children in the 2010 U.S. Decennial Census.” Center for Survey Measurement Study Series (Survey Methodology #2014-02). U.S. Census Bureau. Available online at http://www.census.gov/srd/papers/pdf/ssm2014-02.pdf
O’Hare, W.P. (2014b). “Historical Examination of Net Coverage Error for Children in the U.S. Decennial Census: 1950 to 2010.” Center for Survey Measurement Study Series (Survey Methodology #2014-03). U.S. Census Bureau. Available online at http://www.census.gov/srd/papers/pdf/ssm2014-03.pdf
O’Hare, W.P. (2015). The Undercount of Young Children in the U.S. Decennial Census. Springer Publishers,https://www.springer.com/gp/book/9783319189161#
U.S. Census Bureau (2022). “National Census Coverage Estimates for People in the United States by Demographic Characteristics,” PES20-G-01, Shadie Khubba, Kista Heim, and Jinhee Hong, https://www2.census.gov/programs-surveys/decennial/coverage-measurement/pes/national-census-coverage-estimates-by-demographic-characteristics.pdf
U.S. Census Bureau (2020). “National Demographic Analysis Tables: 2020,” https://www.census.gov/data/tables/2020/demo/popest/2020-demographic-analysis-tables.html
U.S. Census Bureau (2025). “Modified Age and Race Data from the 2020 Census,“ https://www.census.gov/programs-surveys/popest/technical-documentation/research/modified-race-data.html
*Consultant to the Count All Kids Campaign.
**Dr. O’Hare’s work on this study was funded by The Annie E. Casey Foundation but they are not responsible for the contents of the publication.
***The Census Bureau did not start producing data for Black Alone or in Combination until the 2010 Census.
