The Condorcet Jur(ies) Theorem

David Ahn, Santiago Oliveros

Research output: Working paper


Two issues can be decided in a single general election by a single committee or in two special elections by disjoint committees. Similarly, two defendants can be tried together in a joint trial or tried separately in severed trials. The multiplicity of issues or defendants introduces new strategic considerations. As in the standard Condorcet Jury Theorem, we study environments with common values and incomplete information as the number of voters goes to infinity. The joint trial by a single committee can aggregate information if and only if the severed trials by separate committees can aggregate information. Specifically, suppose that either for the joint trial or for the severed trials there exists a sequence of equilibria that implements the optimal outcome with probability approaching one. Then a sequence of equilibria with similar asymptotic efficiency exists for the other format. Thus, the advocacy of a particular format cannot hinge on pure information aggregation with many signals. A counterpart of the sufficient statistical assumption for a single issue suffices for information aggregation in the severed trials, therefore suffices in the joint trial as well. The equivalence of asymptotic efficiency across formats is maintained even when three or more issues are divided into arbitrary partitions, or when abstention is allowed.
Original languageEnglish
Publication statusUnpublished - 2011

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