Majoritarian democracy undermines truth-finding in deliberative committees

Abstract

The aggregated judgments of many usually outperform individual estimates of vaguely known facts. Communication among individuals may, however, undermine this wisdom-of-crowd effect because it makes judgments mutually dependent. Deliberative democratic theory, on the other hand, suggests that communication promotes correct decisions. We investigate this puzzle about the positive and negative consequences of consensus formation on the wisdom of crowds using experimental methods. Subjects in small deliberative committees had to communicate and thereafter judge vaguely known facts. We varied the agreement rules in groups and compared the groups’ change of performance from initial to final estimates. Interestingly, groups’ performance worsened on average when they had to reach a majority decision. Groups came on average closer to the truth if they had to decide unanimously or if they did not have any restrictions to reach agreement. The low performance under majority rule is robust against different knowledge questions, group sizes and communication types. The majority rule may be worst because it makes people too focused to reach a majority so that valuable minority opinions are disregarded or not even voiced. This implies that majoritarian democracy may be less suitable for truth-finding than less or more restrictive quorum rules.