Interrelationship Digraph Method

First, you will need to decide what is the central issue or problem that your digraph will address. Then, you should brainstorm as many related issues or sub-issues as possible. Your central issue should be specific enough that you do not end up with too many related items. This tool is most effective when there are between 15 and 50 items on the digraph.

The next step is to determine the relationship of the items. You should consider each item in relation to every other item on the digraph. It is not enough to simply determine that a relationship exists. You should also decide whether the item is affected by, or causes (even partially) the other item. For every discovered relationship, you should draw an arrow connecting the two items. The arrowhead should point towards the item that is being affected.

Learn more about the Quality Improvement principles and tools for process excellence in Six Sigma Demystified (2011, McGraw-Hill) by Paul Keller, or his online Green Belt certification course ($499).