Fishbone Diagram
Group causes into the standard categories, branch down to root causes, and keep the evidence attached to each bone.
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- Nothing in the chart yet. Start at the top and work down.
Frequently asked questions
The questions people actually ask about this document.
- What is a fishbone diagram?
- A way of laying out everything that might be contributing to one problem, grouped so that the groups stop you stopping too early. The effect goes on the right, the categories branch off a spine, and the causes hang off those. Kaoru Ishikawa formalised it at Kawasaki in the 1960s, which is why it is also called an Ishikawa diagram.
- Which categories should I use?
- The manufacturing default is the six Ms: people, process, equipment, materials, measurement, environment. For services, people, process, policy, place, product and procedure fits better. They are prompts, not a taxonomy: their job is to stop a session producing eight causes that are all about people, which is what an unstructured session almost always produces.
- How far down should it go?
- At least one level past the obvious. A cause with nothing under it is a label, and the useful answers are nearly always one or two whys below the first one somebody says out loud. Two or three levels is plenty; past that you are writing a report rather than finding a cause.
- How do I tell a cause from a symptom?
- Ask whether removing it would change the effect. The orders are late because the picking list is wrong is a cause; the orders are late because the warehouse is behind is the same sentence twice. If the answer restates the problem in different words, you have a symptom, and the cause is whatever is underneath it.
- We have thirty causes. What do we do with them?
- Pick the few that are both likely and worth testing, and go and find out. A fishbone generates hypotheses; it does not rank them, and nothing in the drawing tells you which branch is the real one. The usual next step is to measure two or three, which is also why the evidence line beside each cause is worth filling in as you go.
- How is it different from five whys?
- Five whys follows one chain down. A fishbone spreads sideways first and then down, which is what you want when a problem has several contributing causes rather than one root. Most real problems have several, which is also why the single root cause the phrase promises so often turns out to be the one somebody was already looking for.