Measuring Partisan Bias in Single-Member District Electoral Systems

Abstract

In recent decades, the literature has coalesced around either symmetry or responsiveness as measures of partisan bias in single-member district systems. I argue neither accurately captures the traditional idea of an "efficient" gerrymander, where one party claims more seats without more votes. I suggest a better measure of efficiency and then use this new measure to reconsider a classic study of partisan gerrymandering. Contrary to the original study findings, I show that the effects of party control on bias are small and decay rapidly, suggesting that redistricting is at best a blunt tool for promoting partisan interests.

Keywords: redistricting, gerrymandering, partisan bias, electoral systems, elections, American politics