Interrelationship Digraph - a chart showing the relationship between factors. All the factors to be considered are placed in a box on a piece of paper. Then lines are drawn from each box that has an impact on another box to that box (with an arrow pointing in the direction of impact).
This tool is used in complex situations with many factors. It is among the least used tools (and in my experience that is for good reason, it just is not that useful - John). The diagram will show which factors have the largest number of factors that they influence (by counting the number of arrows drawn from the box).