I believe the optimal team size is 4 people

I believe the optimal team size is 4 people when building a team. This count of 4 does not include the project manager. While it is generally said that 4 to 6 people is good, with a maximum of 9, my own trial and error led me to 4.

I will record here what I felt after actually testing this.

■ Considering communication costs

Communication costs can be expressed by the following formula.

n ( n - 1 ) * n is the number of people

Based on this, the calculations are as follows.

1 person = 0
2 people = 2
3 people = 6
4 people = 12
5 people = 20
6 people = 30
7 people = 42
8 people = 56
9 people = 72

In other words, the cost of communication is 36 times higher for a team of 9 people compared to a team of 2.

Therefore, the fewer the number of people, the lower the communication cost.

■ Do not create odd-numbered teams

I believe it is better not to create odd-numbered teams. This is because conclusions are reached by majority vote. With an even-numbered team, opinions may be split during a majority vote, making it impossible to reach a conclusion.

There is a school of thought that suggests using odd-numbered teams to make it easier to decide by majority vote, but I believe that way of thinking confuses the means with the end.

The purpose of work is "to achieve good results", not "to reach a conclusion by majority vote". If opinions are split right down the middle, I believe developing it into a discussion leads to better results.

■ Why 4 people?

Based on the logic above, the candidates for team size are narrowed down to the following.

2 people
4 people
6 people
8 people

Through trial and error, I found that 4 people was the size where discussion was most active. The definition of active is "an environment where everyone speaks equally". As the number of people increases, imbalances such as "people who talk / people who don't" and "people who talk a lot / people who talk little" begin to appear.

In my experience, I felt there was a significant barrier between 4 and 5 people. This is intuitive and lacks evidence, but I speculate that it might be related to the fact that "humans can only process three things at once".

A team size of 4 means that there are 3 people other than yourself. In other words, I suspect it is because it is easy to exchange opinions and grasp the situation with up to 3 people other than yourself (which the brain can process easily).

■ Productivity is high

Based on my actual experience, a team of four performs the best. It makes pair programming easy, and mob programming is also possible.

If there are three or fewer people, you might end up with one person left over during pair programming, or it might not function as a mob. Therefore, I believe four is the minimum team size that allows for such practices, and because communication costs are kept low, productivity tends to be higher.

Furthermore, if there is a volume of tasks that a four-person team cannot handle, I think the solution is simply to create another four-person team.