Gerrymandering or geography? How Democrats won the popular vote but lost the Congress in 2012

Abstract

This article assesses whether the antimajoritarian outcome in the 2012 US congressional elections was due more to deliberate partisan gerrymandering or asymmetric geographic distribution of partisans. The article first estimates an expected seats–votes slope by fitting past election results to a probit curve, and then measures how well parties performed in 2012 compared to this expectation in each state under various redistricting institutions. I find that while both parties exceeded expectations when controlling the redistricting process, a persistent pro-Republican bias is also present even when maps are drawn by courts or bipartisan agreement. This persistent bias is a greater factor in the nationwide disparity between seats and votes than intentional gerrymandering.