Cause and Effect Analysis
Cause and Effect Analysis, the Ishikawa or fishbone diagram, sorts the possible causes of a problem into fixed categories - method, machine, material, manpower, measurement, environment - so a team checks all of them instead of fixing the first plausible one.
Six ribs radiate out from the effect at the centre, one for each category of cause.
Reach for this when…
- A recurring defect keeps getting blamed on 'the machine' without anyone checking the other categories.
- A team jumps to the first plausible cause, fixes it, and the problem comes back.
- You need a structured way to run a root-cause session without it turning into a shouting match.
How to run it
- State the problem precisely as the effect you're investigating.
- Set out the categories: Method, Machine, Material, Manpower, Measurement, Environment.
- Brainstorm possible causes under each category, no filtering yet.
- Ask 'why' on the most plausible causes to go a layer deeper.
- Agree which root causes to test first, and how you'll know if you're right.
A worked example
Situation. At Aisha Al-Balushi's food processor, Al-Balushi Foods in Muscat, Oman, a batch of packaged salsa kept failing seal-integrity checks, and the line supervisor's first instinct was to blame the new sealing machine.
Applied. The team ran a full cause and effect analysis across all six categories. Under Material they found the actual culprit sitting alongside the machine as an equally live suspect: a change of pouch film supplier three weeks earlier that nobody had flagged.
Result. Switching the film back resolved the failures within a day. The machine, the first suspect, was never at fault.
The catch
The six categories are generic manufacturing categories, and they fit a factory floor far better than a service or knowledge-work problem, where teams often have to bend or rename them. The method also generates causes, not evidence - without testing, a fishbone is just an organised list of guesses.
The category that gets skipped fastest in a rushed session is usually where the answer is.
Origin: Kaoru Ishikawa