Multiwinner Elections and the Spoiler Effect

Fuente: arXiv
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Autori principali: McCune, David, Wilson, Jennifer
Natura: Preprint
Pubblicazione: 2024
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author McCune, David
Wilson, Jennifer
author_facet McCune, David
Wilson, Jennifer
contents In the popular debate over the use of ranked-choice voting, it is often claimed that the method of single transferable vote (STV) is immune or mostly immune to the so-called ``spoiler effect,'' where the removal of a losing candidate changes the set of winners. This claim has previously been studied only in the single-winner case. We investigate how susceptible STV is to the spoiler effect in multiwinner elections, where the output of the voting method is a committee of size at least two. To evaluate STV we compare it to numerous other voting methods including single non-transferable vote, $k$-Borda, and the Chamberlin-Courant rule. We provide simulation results under three different random models and empirical results using a large database of real-world multiwinner political elections from Scotland. Our results show that STV is not spoiler-proof in any meaningful sense in the multiwinner context, but it tends to perform well relative to other methods, especially when using real-world ballot data.
format Preprint
id arxiv_https___arxiv_org_abs_2403_03228
institution arXiv
publishDate 2024
record_format arxiv
spellingShingle Multiwinner Elections and the Spoiler Effect
McCune, David
Wilson, Jennifer
Methodology
In the popular debate over the use of ranked-choice voting, it is often claimed that the method of single transferable vote (STV) is immune or mostly immune to the so-called ``spoiler effect,'' where the removal of a losing candidate changes the set of winners. This claim has previously been studied only in the single-winner case. We investigate how susceptible STV is to the spoiler effect in multiwinner elections, where the output of the voting method is a committee of size at least two. To evaluate STV we compare it to numerous other voting methods including single non-transferable vote, $k$-Borda, and the Chamberlin-Courant rule. We provide simulation results under three different random models and empirical results using a large database of real-world multiwinner political elections from Scotland. Our results show that STV is not spoiler-proof in any meaningful sense in the multiwinner context, but it tends to perform well relative to other methods, especially when using real-world ballot data.
title Multiwinner Elections and the Spoiler Effect
topic Methodology
url https://arxiv.org/abs/2403.03228