Using a Density-Variation/Compactness Measure to Evaluate Redistricting Plans for Partisan Bias and Electoral Responsiveness

• Activity Number: 629
• Type: Contributed
• Date/Time: Thursday, August 4, 2011 : 8:30 AM to 10:20 AM
• Sponsor: Social Statistics Section
• Author(s): Thomas R. Belin*+ and Heidi J. Fischer and Corwin Zigler
• Companies: University of California at Los Angeles and University of California at Los Angeles and Harvard School of Public Health
• Keywords: red-state/blue-state ; seats-votes curve ; Texas redistricting controversy ; voter registration ; Maptitude software ; JudgeIt software

Abstract

The clear association between population density and partisan preference in elections suggests that redistricting plans would be better aligned with principles of partisan fairness if there were a deliberate effort to balance population density across legislative districts. To balance population density without sacrificing geometric compactness, we define a density-variation/compactness (DVC) measure that can serve as a one-number summary of a proposed redistricting plan. We use data from California to guide the choice of a DVC measure and evaluate its performance using election data from Texas during the past decade. Using a political-science model relating legislative representation to the proportion of votes received, higher DVC scores corresponded to estimates of partisan bias with smaller magnitude across a range of redistricting scenarios; meanwhile, contrary to expectations that reduced partisan bias would be accompanied by reduced electoral responsiveness, there was no discernible pattern between DVC scores and estimated responsiveness. We conclude that the use of a DVC measure could provide a check on attempts to introduce partisan bias into the redistricting process.