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When a problem keeps coming back, teams usually fix the first cause someone names. The fish keeps swimming. A fishbone diagram slows that reflex down: it makes the team list every possible cause, in categories, before anyone picks one.
What a fishbone diagram is
The fishbone diagram is also called the Ishikawa diagram or cause-and-effect diagram. Kaoru Ishikawa, a Japanese quality engineer, first used it in 1943 with engineers at Kawasaki and made it widely known through his books on quality control in the 1960s. It became one of the basic tools of the Japanese quality movement.
The problem sits at the head of the fish. The bones are cause categories. In manufacturing the classic set is the 6Ms:
- Methods: procedures, instructions, planning.
- Machines: equipment, software, tools.
- Materials: inputs, parts, data.
- Measurement: how you check, count and inspect.
- Manpower (people): skills, training, workload.
- Mother nature (environment): temperature, location, timing, outside conditions.
Service teams often swap these for categories that fit better, such as policies, procedures, people, place and systems.
Fishbone example: late orders at a meal-kit company
Head of the fish: "18% of Monday deliveries arrive after the promised window, against 4% on other days." A precise head keeps the session focused.
Methods: Monday routes are planned on Friday, before weekend orders close.
Machines: the route planning tool does not account for Monday morning traffic.
Materials: a supplier delivers fresh produce late on Monday mornings.
Measurement: "late" is measured at the depot, not at the customer's door.
People: two new drivers start on Mondays each month.
Environment: heavier traffic at the start of the week.
Checking the data shows two causes explain most late orders: routes planned before the order cut-off and the late produce delivery. Fixing those two is the action. The other bones stay on the diagram, to watch.
One-page model visual
The one-page visual
Use this visual as a quick reference. The card in the deck adds the questions and the steps to run the model on your next real question.
How to run a fishbone session in 30 minutes with the card
- Minutes 0 to 5: write the head. What, where, when and how much. "Customers unhappy" is too vague; "refund requests up from 2% to 5% since March" works.
- Minutes 5 to 8: choose the bones. The 6Ms, or categories that fit your work.
- Minutes 8 to 18: brainstorm causes silently. Sticky notes on each bone. For each cause, ask "why does that happen?" once or twice to go a level deeper.
- Minutes 18 to 25: vote on the likely ones. Each person marks three causes they think matter most.
- Minutes 25 to 30: plan the check. For the top two or three: what data would confirm it, and who gets it by when?
The card explains the categories and gives the steps and an example, so the facilitator does not need to draw the fish from memory.
Common fishbone mistakes
- A vague head. If the problem statement has no number or time frame, the causes will be vague too.
- Treating votes as proof. The vote picks what to test. Data decides the root cause.
- Blaming people. "Careless staff" is rarely the root cause. Ask what in the method or system let the error happen.
- Stopping at the diagram. The output is a short list of causes to check, with owners.
Once you have data on the causes, a Pareto analysis ranks them by impact. If the problem is slow output rather than errors, the Theory of Constraints is the better starting point.
Fishbone diagram FAQ
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What are the 6Ms of a fishbone diagram?
Methods, machines, materials, measurement, manpower (people) and mother nature (environment). They are a starting point; use categories that fit your process.
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How do the 5 Whys relate to the fishbone diagram?
The 5 Whys, a technique associated with Toyota, digs deeper into one cause. The fishbone gives breadth across categories. Use the fishbone to collect causes and a few "whys" to get under each one.
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When should I not use a fishbone diagram?
For a one-off problem with an obvious cause, it is overkill. It earns its place when a problem recurs and the team disagrees on why.
From a wall of causes to two checks
The fishbone card holds the categories and the steps, so a root-cause session can start the moment the problem comes up. The Miro board gives the team the fish to fill in together, and the Google Sheets template and Model Dashboard keep the causes, votes and checks in one place. It is one of 50 models in the MBA Tools deck.
