Citation
Nicholas Stephanopoulos & Eric M. McGhee, Partisan Gerrymandering and the Efficiency Gap, 82 U. Chi. L. Rev. 831 (2015).
Abstract
In this Article, the authors introduce a new measure of partisan symmetry called the efficiency gap, which represents the difference between the parties’ respective wasted votes in an election, divided by the total number of votes cast. The efficiency gap captures, in a single number, all of the packing and cracking decisions that go into a district plan. It is rooted in the insight that partisan gerrymandering is always carried out by cracking a party’s supporters across many districts — where their preferred candidates lose by narrow margins — or by packing them into a few districts — where their preferred candidates win by overwhelming margins. In both cases, the targeted party wastes more votes than its opponent, and it is this disparity that the efficiency gap measures.
The authors compute the efficiency gap for congressional and state house plans from 1972 to 2012. Over this period as a whole, the typical plan was fairly balanced, but in recent years — peaking in the 2012 election — plans have exhibited steadily larger and more pro-Republican gaps. The Article also shows how the efficiency gap could be incorporated into a workable legal standard for partisan gerrymandering.