Widespread Partisan Gerrymandering Cancels Nationally, but Reduces Competition

• In Event: Redistricting, Gerrymandering, Competition and Representation in the USA

Abstract

Congressional district lines in many U.S. states are drawn by partisan actors, raising concerns about gerrymandering. To isolate the partisan effects from the effects of other factors including geography and redistricting rules, we compare possible party compositions of the U.S. House under the enacted plan to those under an ensemble of alternative simulated plans that serve as a non-partisan baseline. We find that partisan gerrymandering is widespread in the 2020 redistricting cycle, but most of the electoral bias it creates cancels at the national level, giving Republicans two additional seats on average. Geography and redistricting rules separately contribute a moderate pro-Republican bias. Finally, we find that partisan gerrymandering reduces electoral competition and makes the partisan composition of the U.S. House less responsive to shifts in the national vote.

Authors

• Christopher Kenny, Harvard University

• Cory McCartan, Harvard University

• Tyler Simko, University of Michigan

• Shiro Kuriwaki, Yale University

• Kosuke Imai, Harvard University