Project Management guide · Risk, quality and control
Fishbone Diagram: How to Do Root Cause Analysis, With Examples
A fishbone diagram, also called an Ishikawa or cause-and-effect diagram, is a visual tool for finding the possible causes of a problem. The problem sits at the 'head' of the fish and the possible causes are grouped along the 'bones', helping a team look beyond the first obvious explanation.
Key takeaways
- A fishbone diagram maps possible causes of a problem under clear categories.
- Start with a specific, measurable problem statement.
- Use the 5 whys to dig below symptoms.
- Test likely causes with data before acting.
When to use a fishbone diagram
- A defect, delay or complaint keeps recurring and nobody is sure why.
- Several entries in the issue log seem to share a cause.
- A team needs to agree what to investigate before collecting data.
- During a lessons learned review or retrospective.
- As part of project quality management, alongside tools such as Pareto charts and checklists.
The diagram is named after Kaoru Ishikawa, the Japanese quality expert who popularised it.
Common cause categories
Categories are prompts, not rules. Pick the set that fits your work and add or rename bones as needed.
| Category | Typical questions | Common in |
|---|---|---|
| People | Skills, training, workload, handovers? | All projects |
| Methods / process | Is the procedure clear, followed, fit for purpose? | All projects |
| Machines / tools | Equipment, software, environments? | Manufacturing, IT |
| Materials / inputs | Quality of data, parts or information received? | Manufacturing, IT |
| Measurement | Are we measuring the right thing, accurately? | Quality-focused work |
| Environment | Location, conditions, organisational culture? | All projects |
| Management | Priorities, decisions, communication, funding? | Projects and services |
The first six are often called the 6Ms: man (people), machine, method, material, measurement and mother nature (environment).
How to build a fishbone diagram
- Write a clear, specific problem statement in the head, for example 'Release defects found by users doubled in Q2'.
- Draw the spine and add four to seven category bones.
- Brainstorm causes with people who do the work, placing each under a category.
- For each cause, ask 'why does this happen?' and add sub-causes as smaller bones. This is often combined with the 5 whys technique.
- Look for causes that appear in several places or that the team believes are most influential.
- Choose the most likely root causes and test them with data before acting.
- Agree actions, owners and dates, and track them in the issue log or RAID log.
Worked example
Problem: 'Monthly client reports are delivered an average of four days late.' The team's diagram included these causes:
| Bone | Causes found |
|---|---|
| People | One analyst does all reports; no cover when on leave |
| Methods | No agreed cut-off for data; reviews done one after another rather than in parallel |
| Tools | Report template rebuilt manually each month |
| Inputs | Finance data arrives on day 5 instead of day 2 |
| Measurement | Nobody tracks how long each step takes |
| Management | Report deadline not shown in team planning |
Data collected over two months showed that late finance data and manual template work explained most of the delay. The team agreed a day-2 data cut-off with finance and automated the template, then tracked the delivery date in the project status report.
Tips and common mistakes
- Keep the problem statement factual and measurable, not a solution in disguise.
- Involve people close to the work; managers alone often miss real causes.
- Treat causes on the diagram as hypotheses until data supports them.
- Avoid blaming individuals. Look for system and process causes.
- Do not stop at symptoms. Keep asking why until you reach something you can change.
Free templates for this topic
Frequently asked questions
What is a fishbone diagram?
A cause-and-effect diagram that groups the possible causes of a problem into categories, shaped like a fish skeleton.
Why is a fishbone diagram called an Ishikawa diagram?
It is named after Kaoru Ishikawa, who popularised its use in quality management.
What are the 6Ms of a fishbone diagram?
Man (people), machine, method, material, measurement and mother nature (environment). Some teams add management.
What is the difference between a fishbone diagram and the 5 whys?
A fishbone diagram maps many possible causes across categories; the 5 whys drills down one chain of cause. They are often used together.
When should you use a fishbone diagram?
When a problem recurs, its cause is unclear, and you want a team to explore possible causes systematically.
How many categories should a fishbone diagram have?
Usually four to seven. Use whatever categories fit the problem.
Is a fishbone diagram a quality tool?
Yes. It is widely listed among the basic quality tools, along with Pareto charts, histograms, check sheets and control charts.
Can a fishbone diagram be used for project risks?
Yes. It can help identify sources of risk by asking what could cause a threat or opportunity to occur.
What comes after a fishbone diagram?
Validate the likely root causes with data, then agree and track corrective actions.
What tools can I use to draw a fishbone diagram?
A whiteboard works well. Diagramming tools, presentation software and many collaborative whiteboard apps have fishbone templates.
Is a fishbone diagram used in Six Sigma?
Yes. It is commonly used in the analyse phase of Six Sigma projects.