American Community Survey data is not accurate for redistricting, Illinois researcher says

[May 12, 2021]  By Greg Bishop

(The Center Square) – With redistricting hearings wrapped up and lawmakers providing their input in a map room controlled by Democrats, it’s unclear when draft maps will be released. But some worry about the accuracy of the data that could be used.

Sherri Taylor, a researcher with the Center for Governmental Studies at Northern Illinois University, said Illinois is in the same pickle as the rest of the country. Census data used to accurately draw new political boundaries for states across the country has yet to be released.

Some Census data has been released for the map-making process, but not the block-level data needed to accurately depict the latest counts. That’s not expected until this summer.

Data from the American Community Survey could be problematic.

“Because it’s only a sample survey there’s a high margin of error with that information,” Taylor said. “So, if you want to look at small cell sizes of say age groups, so you’re looking at zero through 5-year-olds. There’s only so many zero through 5-year-olds that got into that sample survey in Illinois and so the margin of error may be too large, which renders that data unreliable.”

The ACS data becomes more unreliable the further tuned in on a local level for review.

“You can’t even get to the blocks,” Taylor said. “The lowest geography is what you call the block groups which takes a bunch of blocks and puts them together.”

But even that’s not reliable. Then there’s the Census Tract data that could be used.

“They could use those temporarily and then tweak those boundaries later on once the block data is available,” Taylor said.

Block-level data from the U.S. Census has been delayed because of the pandemic and isn’t expected to be released until after a June 30 deadline Democrats at the statehouse are eyeing to pass a map for the governor’s approval.

Republicans at the statehouse have been raising concerns about what data majority Democrats will use for their draft maps.