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Unpublished Paper
Miscounts, Duverger's Law and Duverger's Hypothesis
  • Mattias K Polborn
  • Matthias Messner, Bocconi University
We analyze plurality rule and runoff rule voting games when the vote counting technology is imperfect and each ballot is miscounted with probability $\varepsilon>0$. A strategy profile $s$ is a {\it robust} equilibrium if there is a $\overline \varepsilon >0$ such that $s$ is an equilibrium whenever $\varepsilon <\overline \varepsilon$. We show that all robust equilibria of plurality voting games satisfy {\it Duverger's Law}: In any robust equilibrium, exactly two candidates receive a positive number of votes. Moreover, robustness (only) rules out a victory of the Condorcet loser. All robust equilibria under runoff rule satisfy {\it Duverger's Hypothesis}: First round votes are (almost always) dispersed over more than two alternatives. With three candidates, robustness has strong implications for equilibrium outcomes under runoff rule: For large parts of the parameter space, the robust equilibrium outcome is unique.
  • strategic voting,
  • voting schemes,
  • equilibrium refinement,
  • trembling hand perfection
Publication Date
Citation Information
Mattias K Polborn and Matthias Messner. "Miscounts, Duverger's Law and Duverger's Hypothesis" (2011)
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