Fishbone diagram

Category: Risk identification & assessment · Reviewed by Tim Roche, Director · PI & Commercial · Last reviewed

Fishbone diagram

A fishbone diagram (also Ishikawa or cause-and-effect diagram) is a visual root cause analysis tool that organises possible contributing causes of an effect under category headings on the “bones” of a fish skeleton. It was developed by Kaoru Ishikawa in the 1960s as a quality management tool.

Common category sets

For manufacturing — the 6Ms: Manpower, Machine, Method, Material, Measurement, Mother Nature.

For services — the 4Ps: People, Process, Policy, Plant.

For healthcare — Patient, Provider, Process, Equipment, Environment, Policy.

Each category sprouts sub-bones with specific candidate causes.

When to use

• During a structured root cause analysis workshop.
• When multiple plausible contributing causes need to be visualised at once.
• As an input to a Pareto analysis (identifying the few causes responsible for most of the variation).

Limitations

• Identifies possible causes but does not prove them — verification by data is required.
• Can become cluttered and lose focus on complex problems.
• Output depends heavily on the diversity of the workshop participants.

References

• Ishikawa, K. (1976). Guide to Quality Control. Asian Productivity Organization.
• IEC 31010:2019, Annex B.16.
• ASQ (American Society for Quality). Fishbone Diagram.

Cross-references

• Ishikawa diagram
• Root cause analysis
• Five Whys

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