Fishbone Diagram
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A fishbone diagram organizes potential causes of a problem into categories, visually structured like fish bones around a spine.
Definition
A fishbone diagram (also called Ishikawa diagram or cause-and-effect diagram) is a visual tool for organizing potential causes of a problem into logical categories. The diagram resembles a fish skeleton: the problem statement forms the "head," major cause categories form the "bones" branching off the spine, and specific causes are listed along each bone. Common categories include the 6Ms (Man, Machine, Method, Material, Measurement, Mother Nature) for manufacturing, or 8Ps for services. The visual structure ensures comprehensive exploration of possible causes before jumping to conclusions.
Examples
A team investigating a defect issue created a fishbone diagram with 6M categories. Under "Machine," they listed tool wear, calibration drift, and vibration. Under "Method," they listed sequence changes and operator technique. The visual helped the team see all possibilities before narrowing to the actual root cause through investigation.
Key Points
- Fishbone diagrams organize brainstorming, ensuring comprehensive coverage
- Categories prevent tunnel vision on obvious causes
- The diagram is a hypothesis generator; causes must still be verified
- Visual structure facilitates team discussion and alignment
Common Misconceptions
The fishbone diagram identifies the root cause. The diagram organizes potential causes for investigation. It doesn't prove causation—that requires data, verification, and deeper analysis like 5 Whys.
All causes on the diagram are real. Causes listed are hypotheses to investigate. Many will be eliminated. The diagram's value is ensuring nothing is overlooked, not confirming every listed cause.