Some group decisions require a two-thirds or three-quarters majority of the people voting; others require only a simple majority. Does the accuracy of a group's decision making depend on which majority rule is used? A signal detection theory analysis was used to answer this question. Each member of a group was presented with a noisy display of either a signal or a nonsignal, and then each member cast a yes or no vote for the existence of a signal. The group decision was determined by a majority rule of the members' votes. Normative groups and groups of 5 or 7 people exhibited the same behavior: Performance was best when the group used a simple-majority rule and decreased when the group used more stringent rules. The worst performance was produced by a unanimous rule. Some group members adopted more liberal response criteria when the majority rule was made more stringent.
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