Preference Monotonicity and Information Aggregation in Elections


  • Sourav Bhattacharya

    1. Dept. of Economics, University of Pittsburgh, 4528 Posvar Hall, 230 South Bouquet St, Pittsburgh, PA 15260, U.S.A.;
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    • I thank Daron Acemoglu, David Austen-Smith, Steven Callander, Joyee Deb, Tim Feddersen, Roger Myerson, three anonymous referees, and many participants in various seminars, and conferences for important inputs while writing this paper. All responsibility for any errors remaining in the paper is mine.


If voter preferences depend on a noisy state variable, under what conditions do large elections deliver outcomes “as if” the state were common knowledge? While the existing literature models elections using the jury metaphor where a change in information regarding the state induces all voters to switch in favor of only one alternative, we allow for more general preferences where a change in information can induce a switch in favor of either alternative. We show that information is aggregated for any voting rule if, for a randomly chosen voter, the probability of switching in favor of one alternative is strictly greater than the probability of switching away from that alternative for any given change in belief over states. If the preference distribution violates this condition, there exist equilibria that produce outcomes different from the full information outcome with high probability for large classes of voting rules. In other words, unless preferences closely conform to the jury metaphor, information aggregation is not guaranteed to obtain.