Approval with Runoff

TL;DR

This paper introduces runoff voting rules based on approval ballots, analyzes their properties through axiomatic methods, and evaluates their performance on single-peaked and real-world data.

Contribution

It proposes a family of runoff rules derived from approval-based committee rules and studies their axiomatic properties and practical outcomes.

Findings

Runoff rules can be effectively derived from approval-based committee rules.

Axiomatic analysis reveals desirable properties of the proposed runoff rules.

Empirical evaluation shows the rules perform well on real and single-peaked data.

Abstract

We define a family of runoff rules that work as follows: voters cast approval ballots over candidates; two finalists are selected; and the winner is decided by majority. With approval-type ballots, there are various ways to select the finalists. We leverage known approval-based committee rules and study the obtained runoff rules from an axiomatic point of view. Then we analyze the outcome of these rules on single-peaked profiles, and on real data.