A Novel Method For Showing Racially Polarized Voting: Bayesian Improved Surname Geocoding



Section 2 of the Voting Rights Act is one of the most important tools for litigants challenging discriminatory voting procedures. The Supreme Court outlined the test governing vote dilution claims—which are claims that an electoral system, process, or procedure weakens a minority group’s ability to elect candidates of their choice—under Section 2 of the Voting Rights Act in Thornburg v. Gingles. The Court held, in part, that Section 2 requires plaintiffs to prove that voting patterns within the challenged jurisdiction are polarized by race, which is called racially polarized voting. Put simply, racially polarized voting means that voters of different races vote cohesively with voters of their race and have opposite electoral preferences of other races. Because vote choice is private and most states do not track the race of voters, social scientists have developed statistical methods to make the evidentiary showing that Gingles requires. These methods are decades old and are often the subject of intense scrutiny in vote dilution trials. In some cases, the size of the jurisdiction and the quality of the voter file and voting records prevent plaintiffs from meeting their burden of proof. Analyzing the presence of racially polarized voting will be one of the most important issues during and after the redistricting cycle currently underway following the 2020 Census. Within the last year, an innovative method adapted from other fields of study called Bayesian Improved Surname Geocoding (BISG) has been applied to racially polarized voting analysis in vote dilution cases and has been approved by a federal district court in New York and the U.S. Court of Appeals for the Second Circuit. BISG has received little scholarly attention in voting rights legal scholarship, but it promises to be a critical advancement in detecting vote dilution. This Article seeks to showcase this method, equipping voting rights advocates, social scientists and governments alike with additional tools to secure equal voting rights nationwide. This Article argues that BISG can be used by voting rights advocates to bolster racially polarized voting analysis when the necessary data is available and of sufficient quality. Further, BISG can be helpful to smaller jurisdictions which might have smaller sample sizes in American Community Survey data or a smaller number of precincts.

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