Dunbar’s number represents a theoretical limit on the number of people in a group that can maintain stable social relationships. Stable social relationships are needed to support application of Agile values, principles and techniques. Dunbar’s number is often quoted as 150 people. However, the limit for any individual group is a not only a reflection limits like Dunbar’s number but also context. If we accept there is some theoretical limit that we can’t scale past such as Dunbar’s number, we need to ask how other project or environmental factors further constrain the maximum number of people working on a problem. Why go to the trouble of scaling up the number of people working a problem? Many Agilistas would suggest that a single small team is optimal. However, many problems will require a larger collation of teams to deliver value and functionality. Additional contextual drivers that modify the theoretical maximum number of people in a group or a team-of-teams include at least four factors. They are:
- Cohesion, or how well people stick together. There are many attributes that can generate cohesion. Examples include: big ideas, goals, nationalities, religions and even corporate identities. Cohesion fosters a common relationship, which helps make groups more willing to put forth effort to achieve an end. For example, it often is hard to achieve a cohesive group when members come from multiple external consultancies. Each organization involved in the group have a different set of organizational goals that will reduce cohesion unless they are subjugated to the project goal. Reducing the number of people below Dunbar’s number makes the use of techniques like peer pressure to institutionalize a project vision to increase cohesion easier.
- Complexity is a measure of the number of properties for a project that are outside of the norm. The complexity of a problem reduces the optimal maximum number of people that can be bear because complexity generally requires either more control and coordination or alternately smaller teams to ensure collaboration.
- Uncertainty occurs when teams are searching for an answer to a business or technical problem. When a team needs to tackle an unknown business problem or new technology research is often required. Research generally is constrained to small teams with specialized skills reducing the optimal maximum group size for this type of endeavor well below Dunbar’s number. As concepts and ideas are discovered they can be rolled out more broadly to be fleshed out, prototyped and implemented increasing the group working on the project closer to Dunbar’s number.
- Dependencies between components often mean that work needs to be single threaded (or at least spread less broadly). Dependencies reduce the number of people or teams that can be effectively leveraged.
The idea of increasing the number of people and teams working on a project often appears to be a mechanism for delivering value more quickly. When adding people to is suggested remember the number of people working on a problem is a constraint than can not be dealt with by linearly increasing the number of people applied to a problem until you reach a limit such as Dunbar’s number. Context directly impacts how large any group can before overhead and other constraints reduce effectiveness. It is often said that you can’t get nine women to have a baby in a month. In addition to Dunbar’s number, context plays an important role in defining overall team size.