The Role of Partisan Gerrymandering in U.S. Elections

Abstract

The literature on partisan bias in U.S. redistricting has emphasized the role of incidental or accidental causes like incumbency and political geography, while questioning the importance of deliberate gerrymandering. I reconsider this settled understanding with a wider range of data, a robust difference-in-differences design, and a new measure of bias called the “efficiency gap” that measures the differential wasted votes of a gerrymander directly. I show that the accepted notion of a null effect for gerrymandering was appropriate for an earlier time period, but that gerrymandering has played a much larger and more durable role in the last two rounds of redistricting. I conclude that it is no longer certain that gerrymandering will play a modest role in the future.

Keywords: redistricting, gerrymandering, political representation, elections, election reform