Voter coordination in elections : a case for approval voting

François Durand (1, 2) , Antonin Macé (3, 4, 5, 6) , Matias Nunez (7)

1 Nokia Bell Labs
2 LINCS - Laboratory of Information, Network and Communication Sciences
3 PJSE - Paris Jourdan Sciences Economiques
4 PSE - Paris School of Economics
5 CNRS - Centre National de la Recherche Scientifique
6 ENS-PSL - École normale supérieure - Paris
7 CREST - Centre de Recherche en Économie et Statistique

We study how voting rules shape voter coordination in large three-candidate elections. We consider three rules, that differ on the number of candidates that voters can support: Plurality (one), Anti-Plurality (two) and Approval Voting (one or two). We show that the Condorcet winner is always elected at some equilibrium under Approval Voting, and that this rule provides better welfare guarantees than Plurality. We then numerically study a dynamic process of political tâtonnement which delivers rich insights. The Condorcet winner is virtually always elected under Approval Voting, but not under the other rules. The dominance of Approval Voting is robust to several alternative welfare criteria and the introduction of expressive voters.

Mots clés: Approval voting; Poisson games; Strategic voting; Condorcet consistency; Fictitious play; Expressive voting

Domaines: Economies et finances

François Durand, Antonin Macé, Matias Nunez. Voter coordination in elections : a case for approval voting. 2023. ⟨halshs-03162184v2⟩