I want to share about the ideal team size, or Dunbar’s number.
It’s the limit on the number of people with whom one can form effective, stable Social Relationships; first published in 1992 by anthropologist Robin Dunbar.
Dunbar noted a correlation between the size of a primate brain and the average social group size. By using the average human brain size and extrapolating from the results of primates, he estimated that humans can comfortably maintain ~150 stable relationships.
The term Social Relationship relates to regular interactions, the ability to recognize another member as part of the group, or are committed to a common goal.
These attributes are very important in Agile projects because they rely on team cohesion to minimize control mechanisms.
Dunbar’s argues that at each level of closeness, we are limited in how many relationships we can have: an average of 5 intimate supportive relationships, 15 close friends and so on. We devote about two-thirds of our time to just 15 people.
Dunbar's number provides a limit to try to avoid letting work become too large to manage.
Based on this, 5 to 9 people is often referred to as the ideal team size, and BU’s should not exceed 150.
Some interesting stats from other research which seems to confirm the 150 number:
A study of the twenty tribal societies with available data showed a mean clan group size of 153
Surprisingly the average number of Facebook friends is 150–200
A 2011 twitter study of 1.7m users found they, maintain a stable relationship with 100–200 individuals
Exchange of Christmas cards in the UK & the maximum network size was about 153.5
2008 survey by The Knot Wedding Network of over 18,000 brides revealed an average wedding guest total of 148
The roman army during the Republic utilized a fighting unit called the maniple with 130–140 solders & officers
Modern military companies tops at about 150
Middle Eastern Neolithic villages dating back to 6000BC usually populated 120–150
in the 1800s an average English village had about 160 residents
Dunbar’s number is somewhat controversial
Some scientists have questioned the relevance of brain size; there are other factors that play a role (e.g. territory size, diet). In fact, they’ve found a bewildering array of correlations between brain size and behavioural traits.
If you are keen, here is an entertaining video of Dunbar discussing his work.
This article was first published here.
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