Measuring Political Gerrymandering

TL;DR

This paper discusses the mathematical measurement of political gerrymandering, focusing on the efficiency gap formula and its implications for legal and political processes in the US.

Contribution

It provides a concise, self-contained overview of the efficiency gap formula and its mathematical analysis in the context of gerrymandering.

Findings

Improved versions of the efficiency gap formula have been proposed.

Mathematical analysis is progressing faster than legal rulings.

The efficiency gap plays a key role in gerrymandering cases.

Abstract

In 2016, a Wisconsin court struck down the state assembly map due to unconstitutional gerrymandering. If this ruling is upheld by the Supreme Court's pending 2018 decision, it will be the fist successful political gerrymandering case in the history of the United States. The efficiency gap formula made headlines for the key role it played in this case. Meanwhile, the mathematics is moving forward more quickly than the courts. Even while the country awaits the Supreme Court decision, improved versions of the efficiency gap formula have been proposed, analyzed and compared. Since much of the relevant literature appears (or will appear) in law journals, we believe that the general math audience might find benefit in a concise self-contained overview of this application of mathematics that could have profound consequences for our democracy.