Groups such as juries with more than seven people are less likely to reach a unanimous decision, according to a new study.

Research suggests that group size is vital for decision-making, with one or two dominant speakers swaying the discussion in larger groups.

Speaking at the British Association Science Festival in Glasgow, Professor Simon Garrod said: "Our research shows that large groups with perhaps 10 or more participants, such as juries, are not a good arrangement for gaining true consensus.

"Smaller groups of up to seven people are much more successful in gaining consensus between participants."

The University of Glasgow professor said that smaller meetings tended to be more interactive.

'Attention limit'

Discussions in larger groups became like monologues, with each speaker broadcasting their views to other participants.

In this scenario, one or two people were likely to take over the discussions, said Professor Garrod.

He believes the same is true for all meetings of more than seven people, including cabinet meetings and business conferences.

"It is probably to do with an attention limit that kicks in at around seven or eight people," Professor Garrod explained.

The research could explain why large juries are more likely to reach a hung decision.

They could be helped to gain consensus more consistently by the use of a professional facilitator, he said.

Mock juries

The research also has applications in business. Professor Garrod suggested that companies seeking an innovative, creative solution to a business problem should limit group sizes to up to seven people.

However, larger groups would be effective where the aim was to inform people of certain information through a team leader.

The research was conducted on groups of five or 10 university students asked to consider a case of plagiarism.

The team plan to conduct further research using mock juries.