A Comparison of Sequential Ranked-Choice Voting and Single Transferable Vote

TL;DR

This paper compares sequential ranked-choice voting and single transferable vote (STV), revealing that sequential RCV often yields different winners and favors excellence over proportionality, with implications for minority representation.

Contribution

It provides the first comprehensive comparison of sequential RCV and STV using simulations and real election data, highlighting their differences in outcomes and fairness.

Findings

Sequential RCV often produces different winner sets than STV.

Sequential RCV favors excellence-based outcomes over proportionality.

Sequential RCV may underrepresent minority interests.

Abstract

The methods of single transferable vote (STV) and sequential ranked-choice voting (RCV) are different methods for electing a set of winners in multiwinner elections. STV is a classical voting method that has been widely used internationally for many years. By contrast, sequential RCV has rarely been used, and only recently has seen an increase in usage as several cities in Utah have adopted the method to elect city council members. We use Monte Carlo simulations and a large database of real-world ranked-choice elections to investigate the behavior of sequential RCV by comparing it to STV. Our general finding is that sequential RCV often produces different winner sets than STV. Furthermore, sequential RCV is best understood as an excellence-based method which will not produce proportional results, often at the expense of minority interests.