The science of collective decision-making

September 20, 2007

Why do some juries take weeks to reach a verdict, while others take just hours? How do judges pick the perfect beauty queen from a sea of very similar candidates? We have all wondered exactly why we did not win a certain award. Now, new psychological research explains how groups come to a collective decision.

Jean-François Bonnefon, a University of Toulouse psychologist, conducted the first empirical investigation of the "doctrinal paradox." This occurs when judges, say a hiring committee or a jury, must evaluate several factors about a candidate, (e.g. a possible employee or a defendant in a trial) and come to a majority decision. When different opinions arise, the way they conduct the majority vote can be more important than the opinions themselves.

For example, a seven-judge committee must decide whether to promote a candidate to a position requiring a young, trilingual person. Each judge estimates whether the candidate is young, and whether she is trilingual. In the end, 4 out of 7 judges think she is young and 4 out of 7 think that she is trilingual, but only two of the judges think she is both. How should the committee proceed" They can all vote on the profile, and reject the candidate, or they can vote separately on each criterion and promote the candidate.

Bonnefon investigated which voting procedure was preferred by judges, and how this preference could change in different contexts. He presented the aforementioned situation to over 1.000 participants. Their responses, which are outlined in the September issue of Psychological Science, a journal of the Association for Psychological Science, showed that profile-voting was preferred for simplicity reasons. The preference declined when the criteria were not likely to be simultaneously met by the candidate and the judges were then more likely to adopt criteria-voting.

Bonnefon also points out that "Just as jurors tend to eschew conviction when they lack a clear majority, judges showed some tendency to adopt whichever of the voting procedures that yielded the most lenient decision."

Bonnefon writes that the doctrinal paradox is a "shadowy aspect of the majority rule," and that while the majority rule may be appealing to reach a quick decision, it is also critical to investigate its potential for inconsistencies.
Psychological Science is ranked among the top 10 general psychology journals for impact by the Institute for Scientific Information. For a copy of the article, "How Do Individuals Solve the Doctrinal Paradox in Collective Decisions" An Empirical Investigation" and access to other Psychological Science research findings, please contact Catherine West at 202-783-2077 or

Association for Psychological Science

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