Fishbone diagram

A fishbone diagram is a structured, visual tool used to analyze and display possible causes of a defined problem. It is named for its resemblance to a fish skeleton: the problem statement is written at the “head,” and the main possible cause categories branch off a central “spine,” with more specific contributing factors shown as sub-branches.

In manufacturing Root Cause Analysis (RCA), a team typically:

• States the problem clearly at the right side of the diagram.
• Identifies major cause categories (for example, Methods, Machines, Materials, Manpower, Measurement, Environment) and draws these as main branches from the spine.
• Lists detailed potential causes under each category as smaller branches.
• Reviews, discusses, and narrows down the most plausible causes for further investigation and evidence gathering.

The fishbone diagram does not determine the true root cause by itself; it serves as a structured way to capture and organize hypotheses about why the problem occurs so they can be tested with data and follow-up analysis.