Simulated packing and cracking

TL;DR

This paper introduces simulated packing and cracking to evaluate partisan-gerrymandering measures, revealing that some measures detect these tactics well while others do not, impacting their reliability in analysis.

Contribution

It presents a novel simulation technique for testing gerrymandering measures and assesses their effectiveness in detecting packing and cracking tactics.

Findings

Efficiency gap detects simulated packing and cracking predictably.

Declination records simulated packing and cracking effectively.

Partisan bias and mean-median difference perform poorly in recording these tactics.

Abstract

We introduce simulated packing and cracking as a technique for evaluating partisan-gerrymandering measures. We apply it to historical congressional and legislative elections to evaluate four measures: partisan bias, declination, efficiency gap, and mean-median difference. While the efficiency gap recognizes simulated packing and cracking in a completely predictable manner (a fact that follows immediately from the efficiency gap's definition) and the declination does a very good job of recording simulated packing and cracking, we conclude that both of the other two measures record it poorly. This deficiency is especially notable given the frequent use of such measures in outlier analyses.