Groups: Census privacy tool could hurt voting rights goals

FILE - In this April 1, 2020, file photo, a man wearing a mask walks past posters encouraging participation in the 2020 Census in Seattle's Capitol Hill neighborhood. A delay in census data is scrambling plans in some states to redraw districts for the U.S. House and state legislatures. The Census Bureau has said redistricting data that was supposed to be provided to states by the end of March won't be ready until August or September. (AP Photo/Ted S. Warren, File) (Copyright 2020 The Associated Press. All rights reserved.)

ORLANDO, Fla.A new method being used for the first time by the U.S. Census Bureau to protect people's privacy in 2020 census data could hamper voting rights enforcement and make it harder for congressional and legislative districts to have equal populations, according to a report from two leading civil rights groups.

In test data, the method known as “differential privacy” made smaller counties appear to have more people than they actually did at the expense of more populous counties. It also made counties appear more homogenous than they really are where clear majorities of people have a specific race or ethnic background, according to an analysis conducted by the civil rights groups.

The findings reinforce concerns that differential privacy will lower the quality of the data used for redrawing congressional and legislative districts. They also suggest that the census figures won't support efforts to protect the power of minority voters and comply with court rulings requiring districts to have equal population numbers.

“Our preliminary findings reveal serious concerns about the impact of differential privacy as currently envisioned by the Bureau on our communities’ ability to attain our fair share of political power," said the report by the Mexican American Legal Defense and Educational Fund, also known as MALDEF, and Asian Americans Advancing Justice' AAJC.

The report is the latest warning about the Census Bureau's introduction of deliberate errors to protect privacy into the 2020 census data that will be used for redistricting later this year.

Differential privacy adds mathematical “noise,” or errors, to the data to obscure any given individual’s identity while still providing statistically valid information. Bureau officials said the change is needed to prevent data miners from matching individuals to confidential details that have been anonymized in the massive data release expected as early as August. It will be applied to race, age and other demographic information in geographic areas within each state.

Since it was first proposed three years ago, the methodology has been criticized by redistricting experts and demographers who fear it will create inaccurate data.

Last month, the state of Alabama and Alabama politicians sued the Census Bureau and the Commerce Department, which oversees the statistical agency, claiming differential privacy appeared to erase the Black voting-age populations in 60 communities in Alabama and made 13,000 city blocks appear to have no adults living in them. A three-judge panel was named to hear the Alabama case, which will fast-track it to the Supreme Court if there’s an appeal.