How to build a fishbone diagram
- State the problem as a measurable effect, for example “Shaft diameter out of tolerance on line 3”, not as a cause.
- Brainstorm causes with the team for each category. Write short phrases, one per line.
- For each cause ask “why?” again until you reach a root cause you can act on.
- Mark the most likely causes and verify them with data before you implement a fix.
Where it fits
The fishbone diagram is step D4 (root cause analysis) in an 8D report and part of the Analyse phase in DMAIC. Use a Pareto chart to choose the problem first, and an FMEA afterwards to keep the causes under control.
Frequently asked questions
›What are the 6M categories?
Man (people), Machine, Method, Material, Measurement and Mother Nature (environment). They are the standard categories for manufacturing problems. Service processes often use the 4P or 8P categories instead, and you can rename the categories freely.
›Who invented the fishbone diagram?
Kaoru Ishikawa popularised the cause and effect diagram in the 1960s at Kawasaki shipyards, which is why it is also called an Ishikawa diagram.
›How many causes should a fishbone diagram have?
As many as the team can name in a brainstorming session, typically 3 to 6 per category. The diagram shows possible causes only. The most likely ones must then be confirmed with data before acting.
›Can I use the diagram in a report?
Yes. Download it as PNG for documents and presentations or as SVG for sharp printing and editing in a vector program.