An Ishikawa (fishbone) diagram puts the problem at the head and groups possible causes on the bones.
Key facts
- Also called: fishbone diagram, cause-and-effect diagram, Ishikawa chart.
- Origin: popularised by Kaoru Ishikawa in Japanese quality circles in the 1960s; one of the seven basic quality tools.
- Input: one measurable problem statement, the effect.
- Output: three to five likely causes to confirm with data, not a finished answer.
- Time: usually 30 to 60 minutes with the people who do the work.
What is an Ishikawa diagram used for?
An Ishikawa diagram is used to list every plausible cause of a problem before the team decides which one to fix. It makes the group's thinking visible, brings in what operators, maintainers and quality staff each know, and stops the meeting jumping to the first obvious cause. Typical triggers are a recurring defect, a measure that keeps going red on the tier board, a customer complaint, a safety incident, or the root cause step of a CAPA, an 8D or an A3.
What are the parts of a cause-and-effect diagram?
- Head: the effect, written as a specific, measurable problem statement.
- Spine: the horizontal line leading to the head.
- Main bones: the cause categories.
- Small bones: the individual causes, and the sub-causes found by asking why.
What are the 6Ms of an Ishikawa diagram?
In manufacturing, the 6Ms are the usual starting categories:
- Man (people): skills, training, fatigue, staffing, communication.
- Machine: equipment condition, settings, tooling, maintenance.
- Method: procedures, standard work, sequence, handovers.
- Material: raw materials, components, supplier and batch variation.
- Measurement: gauges, calibration, sampling, how the defect is detected.
- Mother Nature (environment): temperature, humidity, lighting, layout.
Some teams add Management and Money to make 8Ms.
Which categories should you use?
| Setting | Common categories |
|---|---|
| Manufacturing and maintenance | The 6Ms (or 8Ms) |
| Service and administration | The 4Ss: surroundings, suppliers, systems, skills |
| Healthcare | Policies, procedures, people, place, equipment |
| Any process | The steps of the process itself, in order |
Choose categories that fit the problem rather than forcing all six. The categories are prompts, not boxes that must be filled.
How do you make an Ishikawa diagram?
- Write the problem statement in the head, with numbers: "Seal failures on 3% of pouches on Line 2 since 1 October", not "quality problems".
- Draw the spine and the category bones on a whiteboard, large sheet or digital board.
- Brainstorm causes under each bone with the people who know the process. Write every idea down; do not argue about them yet.
- Ask why of each cause until it reaches something the team could change, and add the answers as smaller bones.
- Circle the three to five most likely causes by team vote or experience.
- Test those causes with data, observation at gemba or a short trial before acting. The diagram is finished when causes are confirmed, not when it is full.
Who should take part in a fishbone session?
Four to eight people who know the process: the operators who run it, a maintainer, someone from quality and a facilitator who keeps the group on causes rather than blame. Run it at the process or at the team board, not in a distant meeting room, so ideas can be checked on the spot.
Ishikawa diagram example
A food plant sees inconsistent seal strength on pouches. The fishbone session with two operators, a maintenance fitter and the quality lead lists sealing jaw temperature drift after the mid-shift clean (machine), film thickness variation between suppliers (material), an outdated set-up sheet (method) and a pull tester overdue for calibration (measurement). Line data shows seal failures track jaw temperature, so the team runs a 5 whys on that cause, adds a temperature check to the post-clean checklist and watches the failure rate at the next huddles.
Ishikawa diagram vs 5 whys vs Pareto chart
The three tools answer different questions and are often used in sequence:
- A Pareto chart picks which problem to attack first.
- The Ishikawa diagram spreads wide to list the possible causes of that problem.
- The 5 whys drills deep into one likely cause to reach the root. Our 5 whys template sets out the chain.
Together they form the analysis section of an A3 report and the root cause step of root cause analysis.
What are the 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.
- Stopping at "operator error" or "machine fault" without asking why.
Fishbone diagram template
Our fishbone diagram template lays out the six bones with prompts for each, the steps for running the session and a filled manufacturing example.
Further reading: ASQ, Fishbone (Ishikawa) diagram, and Kaoru Ishikawa, Guide to Quality Control (Asian Productivity Organization).