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Glossary

Fishbone Diagram (Ishikawa)

A fishbone diagram — also called an Ishikawa or cause-and-effect diagram — is a visual tool that sorts the possible causes of a problem into categories, so a team can see every contributing factor at once instead of fixing the first thing they notice. Created by Kaoru Ishikawa, it is a staple of root-cause analysis.

A fishbone diagram is a visual way to brainstorm the possible causes of a problem. You write the problem in a box on the right — the fish's head — and draw a spine leading to it, then label branches off the spine with categories of cause. The shape is why it is also called a cause-and-effect diagram; it is named the Ishikawa diagram after Kaoru Ishikawa, the Japanese quality expert who popularised it in the 1960s.1

The usual categories

Most teams start from a standard set of prompts and adapt them. Two common templates:

  • The 6 Ms (manufacturing roots): Method, Machine, Material, Manpower (people), Measurement, and Mother Nature (environment).
  • The 4 Ps (service and admin work): People, Process, Policy, and Plant (or place/technology).

The categories matter less than what they do: they stop a team from anchoring on the first cause that comes to mind, and they make sure people, process and tools all get examined rather than just the obvious culprit.

How it fits root-cause work

A fishbone diagram is for breadth — surfacing every plausible cause before you judge any of them. Once the branches are full, you pick the most likely one and go deep on it, often with the 5 Whys, to trace it to the condition you can change. Used together, the fishbone widens the search and the 5 Whys narrows it.

It is one of the core tools of root cause analysis, and like any of them it only pays off when the analysis ends in a concrete change with an owner and a date — not a colourful diagram that gets filed and forgotten.

  1. American Society for Quality, Fishbone (Ishikawa) Diagram, drawing on Kaoru Ishikawa, Guide to Quality Control (1968). ↩

Frequently asked

Why is it called a fishbone diagram?
A fishbone diagram is named for its shape: the problem sits in a box on the right like a fish's head, with a horizontal spine running to it and category branches angling off like ribs. Kaoru Ishikawa created it, so it is also called an Ishikawa diagram, and because it links causes to an effect it is known as a cause-and-effect diagram too.
What are the categories on a fishbone diagram?
Most teams start from a standard prompt set and adapt it. Manufacturing work often uses the 6 Ms — Method, Machine, Material, Manpower, Measurement and Mother Nature (environment). Service and admin work often uses the 4 Ps — People, Process, Policy and Plant. The categories matter less than their purpose: making sure every type of cause gets examined.
When should you use a fishbone diagram instead of the 5 Whys?
Use a fishbone diagram when a problem could have several causes and you need breadth, so the team examines people, process and tools rather than fixing the first thing noticed. Use the 5 Whys when you have one likely cause and need depth. In practice you run the fishbone first, then drill the chosen branch with the 5 Whys.

Related

Term

Root Cause Analysis (RCA)

Root cause analysis (RCA) is a structured way to find the underlying cause of a problem — not just its symptoms — so a fix stops it coming back. It uses tools like the 5 Whys, fishbone diagrams and Pareto analysis to move from "what happened" to "why", and ends in a change with a named owner and a date.

 Term

The 5 Whys

The 5 Whys is a root-cause technique: you ask "why?" about five times in a row, tracing a problem back from its visible symptom to the underlying cause, so you fix what actually broke instead of the surface effect. Developed at Toyota, it suits single-cause problems and pairs well with a fishbone diagram.

 Term

After-Action Review (AAR)

An after-action review is a short, structured debrief that asks four questions: what was supposed to happen, what actually happened, why was there a difference, and what will we change? Originally a US Army practice, it turns experience into improvement — and works best when it's blameless but accountable.

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