Where it comes from
The diagram is named after Kaoru Ishikawa, who popularised it in Japanese quality circles. It remains one of the basic quality tools because it makes a team's thinking visible and stops the group jumping to the first, most obvious cause.
Common categories
In manufacturing, the 6Ms are the usual starting point:
- Man (people): skills, training, fatigue, staffing.
- Machine: equipment condition, settings, tooling.
- Method: procedures, standard work, sequence.
- Material: raw materials, components, supplier variation.
- Measurement: gauges, calibration, inspection method.
- Mother Nature (environment): temperature, humidity, lighting, layout.
Service and healthcare teams often adapt these, for example using policies, procedures, people and place. Choose categories that fit the problem rather than forcing all six.
How to build one
- Write a specific problem statement in the head of the fish.
- Draw the spine and add the category bones.
- Brainstorm possible causes under each category with people who know the process.
- Ask why for each cause to add sub-branches.
- Mark the causes the team thinks are most likely.
- Test those causes with data or observation at gemba before acting.
Common mistakes
- Treating every cause on the diagram as proven. The fishbone generates hypotheses; it does not confirm them.
- Writing vague causes such as "training" instead of specific ones like "new starters not trained on changeover".
- Building it alone at a desk rather than with the team at the process.
- Starting with a vague problem statement, which produces a sprawling diagram.
Example
A food plant sees inconsistent seal strength on pouches. The team's fishbone lists sealing jaw temperature drift (machine), film thickness variation between suppliers (material), an outdated set-up sheet (method) and a pull tester overdue for calibration (measurement). Data from the line shows seal failures track jaw temperature, so the team focuses its 5 whys and countermeasures there.