2020 Census Data Products: Data Needs and Privacy Considerations Proceedings of a Workshop (2020) / Chapter Skim
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4 Redistricting and Related Legal Uses
4 Redistricting and Related Legal Uses
Pages 45-58
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From page 45... ...
House and is to be delivered to the states by March 31, 2021, is a critically important census data product.1 The session included three speakers: Justin Levitt (Loyola Law School) , who addressed differential privacy in relation to redistricting and other provisions of the Voting Rights Act (VRA)
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From page 46... ...
Levitt discussed census data use cases in terms of accuracy versus privacy pertaining to redistricting, provisions of the VRA outside of redistricting, and other electoral impacts of census data and differential privacy. 4.1.1 Issues in Redistricting Levitt referred to work by David Van Riper (Minnesota Population Center)
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From page 47... ...
The upshot, depending on the value of , seemed to be that adding noise would be unlikely to create a problem for larger congressional districts, but would likely represent a systemic shift towards rural populations. Adding substantial levels of noise, depending on the final , could create a sizable problem in smaller districts, such as city council districts and county commission districts where there were very few people in a county.
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From page 48... ...
Using the 2010 DDP, Levitt looked at relatively small state legislative districts, specifically, the Delaware State House, which has districts of about 15,000 people. Obviously, all of this would be amplified for smaller city council districts or county commission districts.
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From page 49... ...
Even for internal use, Levitt understood that using the predisclosure avoidance decennial would consume some privacy budget, which would mean that less of the privacy budget would be available for the publicly released tabulations. A postdisclosure avoidance decennial would not eat up any more privacy budget, but then the noise would already be baked in for developing ACS weights or for refining ACS results.
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From page 50... ...
4.2.1 Redistricting the City of New Rochelle Beveridge helped draw a redistricting plan for the city of New Rochelle, New York, in 2007 based on 2000 Census data and again in 2011 based on 2010 Census data. New Rochelle, which has about 77,000 people and abuts New York City, is on a four-year cycle for its council districts.
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From page 51... ...
Citizens by Districts for Census 2010 Data and Synthetic Data 6.00% 5.26% 4.84% 5.00% 4.31% 4.00% 3.80% 3.00% 2.00% 1.28% 1.00% 0.69% 0.00% -1.00% -0.57% -0.85% -2.00% -3.00% -4.00% -4.38% -5.00% -4.67% -4.80% -4.93% -6.00% 1 Released 1 Synthetic 2 Released 2 Synthetic 3 Released 3 Synthetic 4 Released 4 Synthetic 5 Released 5 Synthetic 6 Released 6 Synthetic Data Data Data Data Data Data Data Data Data Data Data Data Figure 4.1 Proposed 2011 redistricting plan for New Rochelle, New York, displaying demographic characteristics from 2010 census published data and contrast with deviations from "ideal" (average) size using 2010 Demonstration Data Products ("synthetic" data)
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From page 52... ...
In the majority Hispanic District 1, there was a large percentage change for African Americans. Moreover, the 2010 DDP data reduces the number of African Americans in District 3 while increasing the number of whites, a problem for the majorityminority district that would likely put it below the 50 percent threshold in CVAP data.
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From page 53... ...
Moreover, population counts at the block level and higher geographic levels were kept invariant under the swapping used in 2010. He asked what remedy was available when it was clear that, at least for New Rochelle, the use of differential privacy undermined the determination of equal districts and diluted minority population shares.
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From page 54... ...
While Levitt correctly stated that districts do not have to be exactly equal in population, there is a question of what it means when a district is close to the boundary of a 1 percent total population deviation that is generally deemed permissible for congressional districts.4 McDonald concluded that confidence intervals of some sort were needed. The effort to produce multiple data sets as a way of generating confidence intervals could be helpful, but for legal purposes, the Census Bureau would need to publish measures of uncertainty for different levels of geography.
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From page 55... ...
Indeed, from a simple linear regression line, African Americans were subtracted from precincts with large African American populations and added back into white precincts, confirming what Beveridge showed for New York State. This could be consequential, affecting the ability to provide effective representation for minority communities who might otherwise deserve it.
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From page 56... ...
Also, if running multiple versions of disclosure avoidance to generate a sort of confidence interval might eat up the privacy budget, then people might prefer to get more accurate individual figures. Beveridge suggested that it could be possible and useful to produce additional DDP-type runs with the 2010 Census data using a bunch of different values of , and that these might inform the use of simulated confidence intervals.
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From page 57... ...
Court of Appeals for the Tenth Circuit5 that involved a five-member school district with 2,850 people in each part of the district and a three-member county commission with just under 5,000 people in each district. The Navajo population was just over the 50 percent threshold in the county so, if the census block data were not accurate, it would mean the difference between having two Navajo members on the three-member county commission and potentially having one or even just an "influence district" and not a majorityminority district.
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From page 58... ...
So, he said, it was a "fantasy" to think that a judge would be able to compel the Census Bureau to provide tabulations from the CEF. Levitt replied that the lawyers of today know never to call any legal outcome a "fantasy." He agreed that Garfinkel had correctly stated that the statute appears to flat out block access to the raw census data, but Levitt also agreed with Beveridge's points that judges and courts interpret statutes differently, as they see fit.
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