Thread by @ElectProject

For the census data nerds, Alabama's challenge to differential privacy is 👀

https://twitter.com/hansilowang/status/1369744488382496771

Differential privacy is essentially the fuzzing of data in order to prevent someone from being able to infer individuals' census responses from the released aggregated data. An analogy is perhaps figuring out the individual numbers in a Sudoku puzzle

Why this matters to the census is the Census Bureau stated it interprets the confidentiality provisions of individuals' responses to the census found in Title 13 of the U.S. code to require data fuzzing

Differential privacy is a particular method of data fuzzing. In theory, essentially random noise is injected into the data, kind of like the margin of error arising from sampling in a poll

But adding random noise to data can create zero or negative population numbers. What Alabama should also challenge is what the Census Bureau calls the "post-processing" to ensure population numbers can't be zero or negative

The differential privacy/post-processing data fuzzing is potentially creating problems that might result in broad bipartisan support for Alabama's lawsuit. These problems aren't too evident when you're working with these data at the state, congressional districts, counties, etc.

But when you drill down to the local level, the data fuzzing is creating implausible counts of children, shifts of minority population out of dense racial/ethnic communities, nonsensical housing occupancy rates, Tribal areas with zero population, and on and on

The Census Bureau claims they fixed these problems that became evident late in 2019, but the post-processing adjustment is a black box and the Census Bureau has not demonstrated what improvements they have made to fix data fuzzing problems

I would add the Census Bureau was rightfully concerned another federal agency like ICE could do a re-identification attack on the aggregate citizenship data to target the deporting of people, but since the Census Bureau will no longer release citizenship data, the issue has waned