A fishbone diagram — also called an Ishikawa diagram after the engineer who popularised it — is a tool for root-cause analysis. When something is going wrong, it helps a team think through all the possible causes in an organised way, rather than fixating on the first explanation that comes to mind.
It is called a fishbone because of its shape: the problem sits at the "head" on the right, and possible causes branch off a central spine like bones, grouped into categories.
How it is structured
- The head — the problem or effect you are investigating, stated clearly. "Invoices are frequently sent late."
- The spine — the horizontal line leading to the head.
- The bones — major categories of causes branching off the spine.
- Sub-bones — specific possible causes within each category.
Common cause categories
A widely used starting set of categories (sometimes called the "6 Ms," though you adapt them to your context) is:
- People — skills, training, communication, staffing.
- Process — the steps, the workflow, the procedures.
- Technology / Machine — systems, tools, equipment.
- Materials / Information — the inputs, data quality, documents.
- Environment — the surrounding conditions, workspace, external pressures.
- Measurement — how things are measured, targets, metrics.
For a business or software context, BAs often simplify to categories like People, Process, Technology, Data, and Policy.
Why it works: without structure, problem-solving tends to chase the loudest or most recent cause. The fishbone forces you to consider every category, which surfaces causes a quick discussion would have skipped. Often the real root cause hides in a category nobody initially suspected.
How to run a fishbone analysis
- State the problem precisely at the head. Vague problems give vague analysis.
- Agree the categories with the team.
- For each category, ask "what here could be contributing to the problem?" and add the causes.
- For each cause, ask "why?" again to go deeper — a cause often has a cause behind it.
- Once mapped, identify the most likely root causes and investigate those with evidence.
A fishbone in words
Problem (head): Customer complaints take too long to resolve.People: not enough trained agents · unclear ownership.
Process: complaints logged manually · no escalation path.
Technology: no tracking system · separate tools per team.
Data: customer history scattered across systems.
Looking across categories, a pattern emerges: the lack of a single tracking system shows up in several branches — a strong candidate for the root cause.
Practice pointer: pair the fishbone with the "5 Whys" — for any cause you list, ask "why?" up to five times. The fishbone gives you breadth across categories; the 5 Whys gives you depth within each.