Judges hear arguments over Census’ contentious privacy tool

Kim Chandler and Mike Schneider/AP

Updated: May 3, 2021 / 03:44 PM CDT

FILE – Rows of homes, are shown in suburban Salt Lake City, on April 13, 2019. Utah is one of two Western states known for rugged landscapes and wide-open spaces that are bucking the trend of sluggish U.S. population growth. The boom there and in Idaho are accompanied by healthy economic expansion, but also concern about strain on infrastructure and soaring housing prices. (AP Photo/Rick Bowmer, File)

MONTGOMERY, Ala. (AP) — The fight over whether the U.S. Census Bureau can use a controversial statistical technique to keep people’s information private in the numbers used for drawing political districts on Monday went before a judicial panel which must decide if the method provides enough data accuracy.

A panel of three federal judges was hearing arguments on whether the method known as “differential privacy” meets the federal legal requirement for keeping private the personal information of people who participated in the 2020 census while still allowing the numbers to be sufficiently accurate for the highly-partisan process of redrawing congressional and legislative districts.

Because a panel of three federal judges will decide the matter, any appeal could go straight to the Supreme Court.

This first major challenge to the Census Bureau’s use of differential privacy comes in the lawsuit filed by the state of Alabama and three Alabama politicians over the statistical agency’s decision to delay the release of data used for drawing congressional and legislative districts. Normally, the redistricting data is released at the end of March, but the Census Bureau pushed the deadline to sometime in August, at the earliest, because of delays caused by the pandemic.

Alabama claims the delay was caused by the bureau’s attempt to implement differential privacy, which the state’s attorneys say will result in inaccurate redistricting numbers. At least 16 other states back Alabama’s challenge, which is asking the judges for a preliminary injunction to stop the Census Bureau from implementing the statistical technique. Alabama also wants the agency to release the redistricting data by July 31.

Alabama Solicitor General Edmund LaCour told the judges that the Census Bureau should return to a previous method for protecting privacy where easily identifiable characteristics in a household are swapped with data from another household.

“Small changes matter when you are dividing up power,” LaCour said.

The judges questioned the solicitor general about why Alabama had not tried to stop differential privacy sooner, but LaCour said it was not ready to be challenged until last year and it was not clear earlier how “dangerous” it would be.

Civil rights advocates, state lawmakers, and redistricting experts have raised concerns that differential privacy will produce inaccurate data for drawing districts, and that will result in a skewed distribution of political power and federal funds. They also worry it will make it difficult to comply with sections of the Voting Rights Act requiring the drawing of majority-minority districts when racial or ethnic groups make up a majority of a community.

Differential privacy adds mathematical “noise,” or intentional errors, to the data to obscure any given individual’s identity while still providing statistically valid information. Bureau officials say the change is needed to prevent data miners from matching individuals to confidential details that have been rendered anonymous in the massive data release. In a test using 2010 census data, which was released without the obscuring technique, bureau statisticians said they were able to re-identify 17% of the U.S. population using the information in commercial databases.

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But University of Minnesota demographer Steven Ruggles said in a court filing that would be impossible to do without access to internal, non-public Census Bureau data.

Department of Justice attorney Elliott Davis, representing the Census Bureau, told the judges that previous methods of privacy protection were not robust enough against data miners who could “reverse engineer” the data.

The delay in the release of the redistricting data has sent states scrambling for alternative plans such as using other data, utilizing previous maps, rewriting laws dealing with the deadlines, or asking courts to extend deadlines. The state of Ohio filed a similar lawsuit over the changed deadlines. A federal judge dismissed the case, but Ohio has appealed.