The fishbone diagram is used primarily in the Define, Analyze, and Improve steps of the DMAIC process.

Look for possible cause-and-effect relationships using a fishbone diagram. The purpose of a fishbone diagram is to have experts identify all the input variables that could be causing the problem of interest. Once we have a complete input variables list, we must attempt to identify the critical few key process input variables (KPIVs) to measure and further investigate.

The fishbone diagram is the preferred Six Sigma tool for identifying what should be sampled in a process and which variables need to be kept in control during the sampling process. Without the kind of cause-and-effect analysis the fishbone diagram supports, the sampling would be less focused.

Sometimes just the process of doing the fishbone diagram leads to the solution, because you are getting the experts together to discuss the problem with a specific focus.

Use of the fishbone diagram use is not limited to manufacturing. Virtually any problem can be tackled using this powerful tool.