3:1 Nesting Rules in Redistricting

TL;DR

This paper investigates the effect of 3:1 nesting rules in redistricting on election outcomes, finding minimal impact on seat distribution and that House seat bias does not strongly influence Senate results.

Contribution

It introduces a comparative analysis of redistricting ensembles with and without nesting constraints using Markov Chain Monte Carlo methods.

Findings

3:1 nesting rule has minimal impact on seat distribution

Extreme House seat bias does not significantly affect Senate seat outcomes

Nesting constraints do not substantially alter the ensemble of possible maps

Abstract

In legislative redistricting, most states draw their House and Senate maps separately. Ohio and Wisconsin require that their Senate districts be made with a 3:1 nesting rule, i.e., out of triplets of adjacent House districts. We seek to study the impact of this requirement on redistricting, specifically on the number of seats won by a particular political party. We compare two ensembles generated using Markov Chain Monte Carlo methods; one which uses the ReCom chain to generate Senate maps without a nesting requirement, and the other which uses a chain that generates Senate maps with a 3:1 nesting requirement. We find that requiring a 3:1 nesting rule has minimal impact on the distribution of seats won. Moreover, we study the impact the chosen House map has on the distribution of nested Senate maps, and find that an extreme seat bias at the House level does not significantly impact the distribution of seats won at the Senate level.