The Is-Is Not matrix is an excellent problem solving tool that can help generate clues and lead you to the root cause of your problem. It was developed by Kepner-Tregoe and identifies where to start looking for causes. By asking simple who, what, when, and where questions it can help you narrow your investigation to factors that have a significant impact on the process/product.
I have used the Is-Is Not matrix on many occasions with great success. One problem concerned a customer having a problem with a plant who supplied them some defective product. Using the Is-Is Not matrix the team was able to determine the root cause of the problem in less than 2 hours. Another problem concerned a spike in warranty for a product. The team determined that the problem originated right after the start of model change. They kept asking themselves “what changed in the process/product?” In a few days, the release engineer determined that a slight product change had been made. Within a few hours, the team determined the root cause of the warranty spike.
The matrix has three columns. The first is the Is column, where you describe what does occur. The second column is the Is Not column, where you describe what does not occur, although it reasonably might. The last column is the distinction column, where you look for differences between the first two columns. There are many text and articles that explain how to use the matrix. One source is The Quality Toolbox, by Nancy Tague. The Is-Is Not matrix is a tool that should be included in any problem solver’s toolkit.