Artificial Partisan Advantage in Redistricting

Abstract

I propose a measure of artificial partisan advantage in redistricting. Redistricting is the process of drawing electoral district maps. Electoral outcomes depend on the maps drawn. The measure I propose compares the share of seats won by a party to the share of the population that lives in jurisdictions (counties and towns) won by this party. If a party has a larger share of seats than the share of the population in jurisdictions in which the party won most votes, then the drawing of the electoral maps conferred an artificial advantage to this party. This measure takes into account the geographic sorting of partisan voters and is simple to compute. Using U.S. election data from 2012 to 2018, I find an artificial partisan advantage of seventeen House seats to the Republican party. I argue that the artificial partisan advantage in the congressional maps of North Carolina, Utah, Michigan and Ohio is excessive.