Juries that have 12 people find it too difficult to reach unanimous verdicts, according to research from Scotland. A maximum of seven to nine people gives a better chance of reaching consensus.
Groups of 10 or more are not good at reaching agreement because different interpersonal behaviour comes into play when this number is reached or exceeded. The findings come from an in-depth study of group behaviour by Prof Simon Garrod of the University of Glasgow, presented yesterday at the British Association meeting in Glasgow.
"A jury of eight or nine is better than 12 in terms of achieving consensus," Prof Garrod said.
Prof Garrod noted that Scottish juries have 15 people. "When you get up to 15 you really have too large a group to reach consensus." He said the smaller number was better unless the group was using a "facilitator" to ensure the individual engagement of all jurors.
The study looked at the group dynamics in different sized mock juries. It shows that in any collection of people a small number emerge as dominant speakers, taking over more of the talking time.
This means that the quieter members of the group tend not to become fully engaged in the decision-making. Prof Garrod acknowledged that these dominant individuals could also lead in a smaller group. "I would think that is true of any group," he said.
The results from this study apply to other decision-making group situations, especially in business, said Prof Garrod. Innovative, creative business solutions are best tackled by small groups while the larger groups are better for giving out information.