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