Dave Gray has been doing some terrific blogging at Communication Nation.  In this post, he shares the results of a study about how people create visual diagrams.

A 1997 study found that when people create visual diagrams, they use about 6 to 12 visual elements, or "nodes" to describe a system.

What's interesting to me is that this is true no matter what tools they used and regardless of the complexity of the system.

Dave suggests that the ways people create diagrams is related to the ways people understand diagrams from others.  His thoughts:

1. People construct "mental models" when trying to understand how things work

2. Most mental models seem to be made up of 6-12 components

3. A diagram with more then 13 components will probably not become integrated into people's consciousness as a mental model

To me, that means that if you want your system to be understood and integrated into people's thinking as a mental model, you had better boil it down to a simple picture.

If you are a lawyer that uses diagrams to communicate with clients (or juries), you should take another look at your materials and see if you can simplify them.  Maybe Bill Gates should take the same advice:

In this slide alone, I count almost 40 components — and I’ve seen a lot of trial graphics that are a whole lot worse.