By Mona Chalabi

In the last census, 9% of black people in the US were missed, and those missing data points mean missing dollars. Imagine you’re trying to count every single person living in the United States. There are two main ways that you can mess up; you can count some people twice and you can miss some people out.

In 2010, the Census Bureau made both mistakes, as it always does, because counting people is hard. It double-counted about 3% of people and omitted another 3% and, because those mistakes work in opposite directions, the overall population count was almost perfectly accurate.

What’s revealing though is who gets counted twice and who gets left out altogether. That’s where race has historically played a big role in government numbers.

The mammoth task of conducting the 2020 US census is already under way, but last time 9% of black people in the US were simply missed, a rate that was higher than any other racial or ethnic group.

The Census Bureau also double-counted 4% of black residents and were able to make educated guesses about another 3%, so they were left with a net undercount of 2%.

There are many reasons why people are missed by the Census Bureau. Residents can be hard to contact (for example, if they live in inaccessible places), hard to interview (if they have limited English proficiency), hard to locate (if they are homeless or have been displaced by a natural disaster) and finally, hard to persuade (people who are angry or distrustful of government can fall into this group). Many of these obstacles are likely to be higher for non-white residents of the US and so people of color are systematically undercounted.