Allen, Christopher. "The Dunbar Number as a Limit to Group Sizes". Life With Alacrity. 2004. Accessed 2018-11-26.

• Dunbar's Number (150) useful for geographically close groups
• Raph Koster's research in online groups suggests 60 natural for online groups
• Hackman indicates 5 best for high-performance teams such as those using Scrum empirical process control
• Scrum rule: 7 +/- 2 (5 to 9) with all essential skills covered among the group tackling the project (no need to seek outside help to get job done)