Fishbone Diagram Helps Relate Inputs (x’s) to The Output (Y)

The fishbone diagram, or more formally called the Cause-and-Effect Diagram, was first developed by Dr. Kaouru Ishikawa in 1943.  It can help you relate the causes, or x’s, to the effect Y.  The effect or output (Y) is what we’re trying to improve and the causes (x’S) are the sources of variation in our process that need to be reduced.  Our goal is to determine the sources of variation that cause the Y to vary the most.

Teams like this tool because it is easy to use.  They can brainstorm various sources of variation and put them into categories or headings in the fishbone diagram.  Common categories may include the 6M’s; Man, Machine, Material, Method, Measurement, and Mother Nature.

The fishbone diagram can be applied in any process; anytime a team is searching for causes.  When using this tool, it is important to keep asking the question, “Why?” over and over.  If the fishbone diagram states the obvious, the team should try again.

When the team has exhausted the ideas for possible causes, they should determine the top 5 or so to further investigate.  Typically some causes will have a greater impact on the effect and the team will have to determine what those are.