Sequential Voting with Confirmation Network

TL;DR

This paper analyzes sequential voting among agents who confirm or unconfirm each other, revealing bounds on how far the selected agent's popularity can be from the most popular, with specific results for approval and plurality voting.

Contribution

It introduces a model of sequential voting with confirmation networks and proves bounds on the popularity ratio of selected agents in different voting systems.

Findings

Approval voting always has a popularity ratio bounded by 2.

Plurality voting can have unbounded ratios, but always has an equilibrium with ratio at most 2.

Certain scenarios can lead to selected agents being much less popular than the most popular.

Abstract

We discuss voting scenarios in which the set of voters (agents) and the set of alternatives are the same; that is, voters select a single representative from among themselves. Such a scenario happens, for instance, when a committee selects a chairperson, or when peer researchers select a prize winner. Our model assumes that each voter either renders worthy (confirms) or unworthy any other agent. We further assume that the prime goal of each agent is to be selected himself. Only if that is not feasible, will he try to get one of those that he confirms selected. In this paper, we investigate the open-sequential voting system in the above model. We consider both plurality (where each voter has one vote) and approval (where a voter may vote for any subset). Our results show that it is possible to find scenarios in which the selected agent is much less popular than the optimal (most popular) agent. We prove, however, that in the case of approval voting, the ratio between their popularity is always bounded from above by 2. In the case of plurality voting, we show that there are cases in which some of the equilibria give an unbounded ratio, but there always exists at least one equilibrium with ratio 2 at most.