David Gurteen

David Gurteen (pictured) is a professional speaker and conversational facilitator. He is the founder of the Gurteen Knowledge Community, a global learning community of more than 22,000 people in 160 countries; the author of Conversational Leadership, an online book; and the originator of the Knowledge Café, in which people come together for unfacilitated conversations on a topic of mutual interest.
The Knowledge Café process
Over the course of 15 years, David has facilitated Knowledge Cafés in more than 30 countries, and has made a discovery that has profound implications for those of us who design and facilitate workshops and collaborative gatherings.

In his article Interactive Dialogue or Serial Monologue: The Influence of Group Size on conversation, David reveals that the ideal group size for unfacilitated interactive conversation is four people. If not four, then five is OK but three is better.

Best: four people.
Second best: three people.
If no other option: five people.

The conversation does not work so well when the group consists of more than five people. One or two people are likely to dominate; the conversation will probably break into two, even three; someone may be excluded from the conversation, and group energy will be low.

Although David made this discovery through a process of trial and error, a research paper confirms some of his findings. Here is the abstract:

Current communication models draw a broad distinction between communication as dialogue and communication as monologue. The two kinds of models have different implications for who influences whom in a group discussion.
The experiments reported in this paper show that in small, 5-person groups, the communication is like dialogue and members are influenced most by those with whom they interact in the discussion.
However, in large, 10-person groups, the communication is like monologue and members are influenced most by the dominant speaker.
The difference in mode of communication is explained in terms of how speakers in the two sizes of groups design their utterances for different audiences.

Source: Group Discussion as Interactive Dialogue or as Serial Monologue: The Influence of Group Size, by Nicolas Fay (University of Glasgow), Simon Garrod (University of Glasgow) and Jean Carletta (University of Edinburgh).

Further reading

Conversational Leadership

Knowledge Café—dedicated website

Knowledge Café tipsheet, by David Gurteen and Steve O’Hagan

Real conversations, by David Gurteen, on LinkedIn