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.
Jason Torchinsky, a lawyer also representing Alabama, said the “little bit of noise” the bureau claims to insert could affect the accuracy of the data and consequently, the number of the state's majority-minority districts, in which racial or ethnic groups make up a majority of a community.
Civil rights advocates, state lawmakers and redistricting experts have raised concerns that differential privacy will produce inaccurate data that will skew the distribution of political power and federal funds.
But Department of Justice attorney Elliott Davis, representing the Census Bureau, told the judges that previous methods of privacy protection, such as swapping information around, are not robust enough to guard against someone being able to “reverse engineer” the data to get people’s information.
Davis said computer power has risen exponentially since the early methods were developed for protecting privacy. The new method used by the Census Bureau protects privacy while providing statistically accurate data, he said.
“The error evens out,” Davis said.
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 information in commercial databases.
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.
The three-judge panel did not indicate when it would rule.
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