# A formula goes to court: Partisan gerrymandering and the efficiency gap

## TL;DR

This paper examines the mathematical properties of the efficiency gap, a formula proposed to detect partisan gerrymandering, discussing its potential and limitations in legal contexts.

## Contribution

It analyzes the efficiency gap's mathematical characteristics and critiques its use, providing insights into its application in court cases.

## Key findings

- Efficiency gap reduces to a proportional comparison of votes and seats.
- The formula has notable mathematical properties and limitations.
- It can be a useful tool but requires careful interpretation.

## Abstract

Recently, a proposal has been advanced to detect unconstitutional partisan gerrymandering with a simple formula called the efficiency gap. The efficiency gap is now working its way towards a possible landmark case in the Supreme Court. This note explores some of its mathematical properties in light of the fact that it reduces to a straight proportional comparison of votes to seats. Though we offer several critiques, we assess that EG can still be a useful component of a courtroom analysis. But a famous formula can take on a life of its own and this one will need to be watched closely.