INFORMATION AGGREGATION BY MAJORITY RULE: THEORY AND EXPERIMENTS1

Although majority rule has limited value for aggregating conflicting preferences, it offers promise for aggregating decentralized information. The Condorcet Jury Theorem (CJT) states that majoritarian collective judgments can improve upon the accuracy of the judgements of the constituent individual voters. Recently, it has been argued that the CJT assumes implicitly that each vote reveals the voter's private information, and that such behavior by all voters is not usually a Nash equilibrium. Some voters may have reason to ignore their private information, and majority rule voting may fail to realize the judgmental synergies predicted. We also prove that there exists a Nash equilibrium at which the information aggregation synergies of majority rule surpass those predicted by the CJT. We report on experiments testing whether (a) the voting by individuals reflects their information, and (b) majority rule generates the synergy predicted by the CJT. The results indicate that the judgmental benefits of majority rule are robust. Groups do better than individuals even in situations in which the attractiveness of non-informative voting should be high