= a Group Tresholds number of 50
Last Supper 13 — "The Judas Number".
A group size of 13 doesn't represent a threshold ideal value, but rather a threshold nadir. It is one of the points where groups can change behavior and risk becoming dysfunctional. There's one of these nadirs beyond every group threshold, where the previously harmonious group dynamics become more difficult. I've chosen to highlight this specific number because it's a point that small communities often hit, particularly as entrepreneurial organizations try to grow above their startup beginnings.
(I should note that 13 isn't a precise number, but rather one offered because it's in the right range and because it's poetically easy to remember. The exact number occurs somewhere between 9 and 25, but I suspect it is worst in the range of 12-15.)
In a group of this community size no one ever feels like they get a fair share of time. Studies show that at this size participants underestimate the amount of time they contributed to the conversation, and thus will come out feeling like they were unfairly ignored despite having a fair share of the conversation. Groups of this size risk people being lumped into categories and ceasing to be trusted as individuals. In addition, problems start with the development of "too many chiefs," yet there is not enough enough variety of non-chiefs for them to direct. Furthermore, multiple leaders may struggle for hierarchical status, increasing the conflict in an already troublesome group.
If your community is unfortunately stuck at this nadir, one of two things usually occurs.
Most commonly, the group shrinks. This could be because participants unhappy with the group dynamics abandon it; or it could occur in a more organized way with the unwieldy large group breaking into two or more smaller groups. For example, a terrible group of 13 could become two more functional groups of 6 and 7.
Alternatively, more energy could be expended. This could be in the form of more formal organization, rewards for participation, or more time to be casual and socialize in order to shake off the tensions of this size group. Though these efforts don't usually change the size of the group, they can improve its dynamics.
Energy could also be spent to help push the group up to the next threshold. Though this could occur naturally — for example if the group focuses on a topic of particular interest that causes new people to continually be added. In addition, in order to grow a group to a new threshold it often requires the efforts of more than one leader to succeed.
A group size of 13 isn't necessarily bad, just more difficult. Anthropological studies show that primitive hunting tribes often temporarily broke into "bands" of this size — my presumption is that the value of having that many people hunting together outweighed the social costs of the group. It is interesting that most juries are made up of groups this size. I believe that the social dynamics of this size of group with all new members creates some tension among the jurors, which may serve justice to make sure that all sides are considered by the jury without falling into groupthink. However, from my experience, the interpersonal conflict in a jury can also slow down the deliberation process and cause much frustration among the participants." (http://www.lifewithalacrity.com/2008/09/group-threshold.html)