Estimating the undercounts and overcounts of the 2020 Census

The decennial census is a big undertaking. And the work continues: the Census Bureau just released their estimates of how well the 2020 counts reflect the population of the United States.

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“Today’s results show statistical evidence that the quality of the 2020 Census total population count is consistent with that of recent censuses. This is notable, given the unprecedented challenges of 2020,” said Director Robert L. Santos. “But the results also include some limitations — the 2020 Census undercounted many of the same population groups we have historically undercounted, and it overcounted others.”

The two analyses are from the Post-Enumeration Survey (PES) and Demographic Analysis Estimates (DA) and estimate how well the 2020 Census counted everyone in the nation and in certain demographic groups. They estimate the size of the U.S. population and then compare those estimates to the census counts…

The results show that the 2020 Census undercounted the Black or African American population, the American Indian or Alaska Native population living on a reservation, the Hispanic or Latino population, and people who reported being of Some Other Race.

On the other hand, the 2020 Census overcounted the Non-Hispanic White population and the Asian population. The Native Hawaiian or Other Pacific Islander population was neither overcounted nor undercounted according to the findings.

Among age groups, the 2020 Census undercounted children 0 to 17 years old, particularly young children 0 to 4 years old. Young children are persistently undercounted in the decennial census.

I can imagine how some might read this story: the Census uses estimates and additional data to make claims about what is supposed to be a comprehensive count? Here are some quick thoughts in response:

  1. The numbers might sound like a lot: an undercount of the total population of 18.8 million? Yet, the error rates for separate groups are reported often between 1-4% and the total is off less than 6%.
  2. If the official numbers are known to be overcounts or undercounts, how might researchers take that into account when using the data?
  3. The Census is using multiple data sources to try to both get the most accurate statistics and improve its methodology. Explaining this publicly hopefully helps builds trust in the process and the numbers.
  4. It will be interesting to see how all of this informs future data gathering efforts. If there are consistent undercounts with certain groups, what changes in the coming years? If other data sources provide useful information, such as vital records, can these be incorporated into the data? And so on.

Collecting data about the population of a large country is no easy task and is a work in progress.

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