Working Paper Abstract
288.Robust Political Equilibria in Plurality and Runoff Voting Gamesby Matthias Messner and Mattias Polborn
A central problem for the game theoretic analysis of voting is that voting gameshave very many Nash equilibria. In this paper, we consider a new refinementconcept for voting games that combines two ideas that appear reasonable for votinggames: First, trembling hand perfection (voters sometimes make mistakes whencasting their vote) and second, coordination of voters with similar interests. Weapply this refinement to an analysis of multicandidate elections under plurality ruleand runoff rule.For plurality rule, we show that our refinement implies Duvergerís law: In allequilibria, (at most) two candidates receive a positive number of votes. For the caseof 3 candidates, we can completely characterize the set of equilibria. Often, thereexists a unique equilibrium satisfying our refinement; surprisingly, this is even true,if there is no Condorcet winner. We also consider the equilibria under a runoff ruleand analyze when plurality rule and runoff rule yield different outcomes.
Keywords: strategic voting, runoff rule, plurality rule, equilibrium refinement, trembling hand perfection, coalition-proofness.
JEL code: D720
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