Root cause analysis · Diagrams · Problem solving
A fishbone diagram example, from problem to root cause
By T. Krause
What does a finished fishbone diagram look like, and how does a team get from fourteen sticky notes to one cause worth fixing? This guide works through a made-up example about late deliveries, then shows how to build your own Ishikawa diagram in six steps.
Most searches for a fishbone diagram example end on a picture. The problem sits in a box on the right, six bones fan out to the left, and each bone carries a few causes. The picture shows what the finished diagram looks like. It doesn't show how the team filled it in or what they did with it afterwards, and that second part decides whether the analysis finds anything.
This guide covers both. It explains what the diagram is and when it's worth drawing, goes through the category sets teams use, and then follows one example from the problem statement to a cause the team can test. The example is made up. It's an online shop whose orders keep arriving late, so you can see every step without anyone's real data.
A note before we start. We make Prompt Board, and our fishbone diagram template uses the same late-delivery problem as its sample board. Everything here works just as well on paper or a wall of sticky notes.
What a fishbone diagram is
A fishbone diagram is a cause-and-effect chart. You write the problem, the effect, at the head of the fish. A line runs back from it like a spine, and bones branch off the spine, one per category of possible causes. Each cause goes on its bone as a short note. When a cause has a cause of its own, it gets a smaller bone off the first one.
You'll also see it called an Ishikawa diagram, a cause-and-effect diagram or a herringbone diagram. They're all the same chart. Kaoru Ishikawa popularised it in the 1960s. He had pioneered quality management processes at the Kawasaki shipyards, and the diagram became one of the seven basic tools of quality control.
What the diagram does well is spread a team's attention. Ask a group why orders arrive late and the loudest theory wins within two minutes. The bones make the group look at people, process, tools and suppliers before anyone settles on an answer.
When to use one
Draw a fishbone diagram when:
- a problem keeps coming back after you fixed what looked like the cause
- the team has agreed on one cause and nobody has checked the others
- an incident review needs to look past the step that failed to the conditions that let it fail
- several departments touch the problem and each one points at another
Skip it when the cause is already known and proven, or when one person can trace a single broken step in ten minutes. A fishbone session costs an hour of several people's time. Spend that hour on problems where the cause is still an argument.
The categories teams put on the bones
The bones are categories, and choosing them is the first real decision. Three sets come up again and again.
Manufacturing, the Ms. The classic set is manpower, machine, material, method and measurement. Many teams add environment as a sixth, often called mother nature, which gives the 6M version you see on most factory templates.
Service, the Ss. Surroundings, suppliers, systems and skills. Some versions add safety as a fifth.
Marketing, the 8 Ps. Product, price, place, promotion, people, process, physical evidence and performance.
Treat these as starting points. They exist so you don't forget a whole area, and teams adapt them to their own work all the time. A software team might use code, infrastructure, process, people, third parties and monitoring. A school might use pupils, teaching, timetable, building and home.
Four to six bones suits most problems. With fewer, the bones get crowded and sorting stops helping. Past seven, half of them stay empty. It also pays to pick categories that match how your organisation is split. If the Suppliers bone belongs to purchasing and the Carriers bone belongs to logistics, the finished diagram tells you who to talk to next.
How to make a fishbone diagram
- Write the problem as an effect you can measure. "Orders arrive late" is a start. "Orders arrive after the promised delivery date" is better, because anyone can check whether a given order counts. Keep solutions out of it. "Not enough packers" is a cause in disguise.
- Draw the head and the spine. The problem goes in a box on the right, with a long arrow pointing at it.
- Choose four to six bones. Start from one of the sets above and rename whatever doesn't fit your work.
- Write causes in silence first. Give everyone five to eight minutes to write possible causes on sticky notes, one cause per note, before anyone talks. Then place them on the bones together. Writing first keeps the first speaker from setting the agenda.
- Ask why again on each cause. For each note, ask why it happens. If the answer is another cause, add it as a smaller bone off the first. Stop when the answer is something the team could change or measure.
- Pick the causes to check, then check them. Vote on the two or three causes that look most likely. Then collect data on those before you fix anything.
Step 6 is the one teams skip. The diagram lists suspects and convicts none of them. A meeting that ends with a fix for the most popular sticky note has made a guess.
A worked fishbone diagram example: late deliveries
Here is the whole process on one problem. The shop, the team and the numbers are invented for this guide.
The situation
A small online shop sells kitchenware and ships from its own warehouse. It promises delivery within three working days. Customer service has been getting more "where is my order?" emails, and a check of last month's orders shows about one in eight arrived after the promised date. The operations lead books an hour with the warehouse lead, a customer service agent, the person who manages suppliers and the developer who looks after the shop system.
The head of the fish reads: Orders arrive after the promised delivery date.
The bones
The team uses six categories that match how the shop runs: People, Process, Tools, Suppliers, Carriers and Data. After eight minutes of silent writing and twenty of placing and discussing notes, the bones look like this.
| Bone | Causes the team wrote |
|---|---|
| People | New pickers not trained on the shelf layout. Two of five packers on holiday in the same week. Nobody owns the queue of late orders. |
| Process | Orders batched for picking only twice a day. Orders placed after 2 pm wait until the next morning. An out-of-stock item holds the whole order back. |
| Tools | Scanner batteries die mid-shift. The label printer jams on the cheaper labels. |
| Suppliers | The most-used box size ran out twice. One supplier delivers a day later than agreed. |
| Carriers | The van arrives before the afternoon batch is packed, so those parcels miss the pickup. Weekend parcels sit at the depot until Monday. |
| Data | Stock counts in the shop system are wrong, so the shop sells items that aren't on the shelf. The promised date ignores bank holidays. |
That's fourteen causes. Some came with a second why attached. Under "An out-of-stock item holds the whole order back", the developer added "stock counts are wrong", which already sits on the Data bone. Under "The van arrives before the afternoon batch is packed", the warehouse lead added "orders batched twice a day" from Process. When one cause keeps turning up under others, circle it. That's a lead.
Narrowing down
Each person gets three dot votes. These three notes collect the most dots:
- Orders batched for picking only twice a day
- Stock counts in the shop system are wrong
- The van arrives before the afternoon batch is packed
Nobody fixes anything yet. The team agrees on one check per cause, each with an owner and a date:
- Warehouse lead: for every late order last month, compare the time it was packed with the time the van left.
- Developer: list the late orders that contained an item the system showed in stock but the shelf didn't have.
- Operations lead: pull a week of order times and count how many came in after the afternoon batch started.
What the data showed
A week later the team meets for twenty minutes. Most late orders were packed after the van had left, and nearly all of those were placed after the afternoon batch had started. The stock-count problem was real but rare, behind a handful of late orders.
So the root cause in this example is the picking schedule. Two batches a day worked when the shop was smaller. At today's order volume, the afternoon batch finishes after the carrier's pickup, and anything ordered after lunch loses a day. The team tries a third picking batch at 1 pm and asks the carrier about a later pickup. Fixing the stock counts goes on the list as a separate, smaller job.
The first theory in the room had been the packers on holiday. It went on the People bone, got one vote, and the data didn't back it up. Without the diagram, the shop might have hired a temp and still missed the van every afternoon.
The same board, ready to edit
The fishbone diagram template on Prompt Board starts from this problem, with the six bones above and one sample note on each. Replace the head with your own problem, rename the bones, and let the team add its notes.
Common mistakes
- A problem statement with the cause built in. "Late deliveries because of the carrier" closes the investigation before it starts.
- Bones named only after departments. If every bone is a team name, the session turns into each team defending itself. Mix in process, tools and data.
- Stopping at the first why. "Scanner batteries die" is a symptom. Why do they die? Nobody charges them overnight, because the charging station is in the office upstairs.
- Fixing the most-voted cause without checking it. Votes show what people believe. Data shows what happened.
Frequently asked questions
What is the difference between a fishbone diagram and the 5 whys?
The 5 whys follows one chain, asking why until you reach something you can fix. A fishbone diagram goes wide first and collects possible causes across several categories. They work well together. Use the fishbone diagram to find the candidates, then run the 5 whys on the two or three the team votes for. Step 5 above is a short version of that.
What are the 6 Ms of a fishbone diagram?
Manpower, machine, material, method, measurement and mother nature, which means the environment. Some teams write people instead of manpower. An 8M version adds management and maintenance.
Is an Ishikawa diagram the same as a fishbone diagram?
Yes. Ishikawa diagram, fishbone diagram, herringbone diagram and cause-and-effect diagram all name the same chart. "Fishbone" comes from its shape and "Ishikawa" from Kaoru Ishikawa, who popularised it.
How many categories should a fishbone diagram have?
Four to six for most problems. Use fewer and the causes pile up on each bone. Use more and some bones stay empty. Start with a standard set and rename or merge categories until each one fits your work.
If a problem has come back twice already, book the hour. Open the fishbone diagram template, write the problem in the head, and have everyone write before anyone argues.