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 reasons (x’S) are the sources of variation in our process that need to be decreased. 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 types may include the 6M’s; Man, Machine, Material, Method, Measurement, and Mother Nature.
The fishbone diagram can be used in any operation, anytime a team searches for causes. When using this tool, it is essential to keep asking “Why?” repeatedly. 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 to investigate further. Typically some reasons will have a more significant impact on the effect, and the team will have to decide what those are.
The team may want to consider the following:
- Is it a cause (not a solution?)
- Can we do anything about the reason?
- Are we pretty sure that it will change the effect?
- Do we agree?