2 - What Happened in 2011? The Other “Great Gerrymander”

Summary

Is partisan gerrymandering widespread in the state legislatures? We assess state legislative redistricting maps approved by state governments in 2011. We find results that are similar to estimates of districting bias in the US House. On average, partisan bias increased after redistricting. State governments approved more than forty state legislative redistricting plans that gave one party an extreme electoral advantage. Although we find a few examples of Democratic gerrymanders with modest levels of bias, most of the extremely biased maps favor the Republican Party. In total, there are nearly two dozen maps that award Republicans 20 percent more of the seats than Democrats when the vote is close. These extreme partisan gerrymanders give Republicans a considerable structural advantage in state legislative elections. We estimate that, in the average state legislative assembly, Republican candidates can expect to win about 9 percent more seats than Democratic candidates would for a given share of the vote, between 45 percent and 55 percent of the vote.