The Condorcet Jur(ies) Theorem

Should two issues be decided jointly by a single committee or in separately by different committees? Similarly, should two defendants be tried together in a joint trial or tried separately in severed trials? Multiplicity of issues or defendants introduces novel strategic considerations. As in the standard Condorcet Jury Theorem, we consider large committees with common values and incomplete information. Our main result is that 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 as the number of voters goes to infinity. Then a sequence of equilibria with similar asymptotic efficiency exists for the other format. Thus, the advantage of either format cannot hinge on pure information aggregation with many signals.