Condorcet's Jury Theorem with Abstention

Ganesh Ghalme; Reshef Meir

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arXiv · 2408.00317

Condorcet's Jury Theorem with Abstention

Ganesh Ghalme·Reshef Meir

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Abstract

The well-known Condorcet's Jury theorem posits that the majority rule selects the best alternative among two available options with probability one, as the population size increases to infinity. We study this result under an asymmetric two-candidate setup, where supporters of both candidates may have different participation costs. When the decision to abstain is fully rational i.e., when the vote pivotality is the probability of a tie, the only equilibrium outcome is a trivial equilibrium where all voters except those with zero voting cost, abstain. We propose and analyze a more practical, boundedly rational model where voters overestimate their pivotality, and show that under this model, non-trivial equilibria emerge where the winning probability of both candidates is bounded away from one. We show that when the pivotality estimate strongly depends on the margin of victory, victory is not assured to any candidate in any non-trivial equilibrium, regardless of population size and in contrast to Condorcet's assertion. Whereas, under a weak dependence on margin, Condorcet's Jury theorem is restored.

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Ganesh Ghalme, Reshef Meir. 2024-08-01. Condorcet's Jury Theorem with Abstention. https://arxiv.org/abs/2408.00317

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