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.

Gender and age are factors too. Black children are twice as likely to be undercounted as children who aren’t black. And, since the US criminal justice system incarcerates black people at five times the rate of white people, prison gerrymandering can occur; young black men will be counted by the census as residing within a prison which inflates the population count (and political representation) of census tracts with prisons and further deprives the black communities where many of those men will ultimately return.

Those missing data points mean missing dollars. In 2017 alone, $1.5tn of federal spending was allocated on the basis of Census Bureau data. That estimate comes from Professor Andrew Reamer at the George Washington Institute of Public Policy. Reamer explains that calculating exactly how many of those federal dollars were lost to black communities specifically would be near impossible because the allocation of funds is based on often complex formulas – but even the crudest of calculations (dividing all that federal money per member of the population) puts the value of filling out a census form at over $4,000.

“Black people have been undercounted since we were counted as three-fifths of a person, 400 years ago,” says Jeri Green, who spent 20 years working as a senior adviser on civic engagement at the Census Bureau. “We have always been undercounted, in stark contrast to the white population that has always been overcounted.”

In 1940, the Census Bureau missed one in every 12 black residents. Since then, the black undercount rate has slowly improved. However, the Census Bureau continues to make larger errors with the black population than with the non-black population. In other words, the racial inequality in national statistics has been stubbornly stable.

Dr William O’Hare, a demographer working with the Census Bureau since 1970, explains that in the 1970s, big city mayors “knew that they were missing out on money because members of their population weren’t being counted properly”.

One such mayor was Maynard Jackson, who became the first black mayor of Atlanta, Georgia in 1973. At the time, the 1970 census had estimated that the city was 51% black but a study in 1975 showed how the black undercount was artificially cutting funding in many cities.

Then, as now, it is hard for officials to respond to the Census Bureau with more accurate figures. But Jackson tried. In the 10 days that Atlanta was given to check their population count in 1980, the mayor’s team was able to find an additional 36,900 residents.

Green now works at the National Urban League where a new campaign, Make Black Count, uses the same icon as a 1970 campaign of the same name. Green understands that police brutality, voter suppression, gentrification and access to healthcare seem like much more pressing concerns but explains that Census Bureau numbers underpin those many forms of injustice. “We believe that right now there is no more important issue facing the black community than being counted and voting.”

Another group seeking to engage the public is the Census Project. Comprising over 800 local, national and state organizations, the Census Project is concerned that, under Donald Trump, the possibility for error has grown – they estimate that there is a $2bn shortfall of budget needed to complete an accurate decennial census.

Moreover, the failed attempt last year to add a citizenship question to the census questionnaire may have deepened distrust, including among communities of color.

“The data on your census form is far less than what you’re giving to Facebook,” Steve Jost, a former Census Bureau employee and consultant to the Census Project explains, “but people do have a concern that government is somehow going to give this information to corporations.”

Black residents will yet again be missed from the national count in 2020 – somewhere between 1.1 million and 1.7 million of them according to the Urban Institute. Unless there is a significant change in either the public funding for the census, or the public’s willingness to fill out these forms, it is likely that millions of dollars in federal funding will be misallocated as a result.