Fishbone diagram
A visual root-cause analysis tool that shows a stated problem at the head and organizes possible causes along branching 'bones' by category, allowing the team to drill down into sub-causes; also known as a cause and effect diagram.
Key Points
- Clarifies the relationship between an effect (problem) and potential causes grouped by category.
- Built through facilitated brainstorming; teams ask "why" repeatedly to add deeper sub-causes.
- Typical categories include Methods, People, Materials, Equipment/Technology, Environment, and Measurement (adapt as needed).
- Supports problem exploration; findings should be validated with data before selecting corrective actions.
Example
During Control Quality on a software project, the team faces recurring login failures. The project manager leads a fishbone (cause and effect) session. Categories include People, Process, Tools, Environment, and Requirements. The team maps sub-causes such as ambiguous acceptance criteria, flaky test environment, missing input validation, and skipped peer reviews. These insights guide targeted experiments and fixes.
PMP Example Question
During a quality review, a project team wants to structure and brainstorm potential reasons for a persistent defect before running experiments. Which tool should the project manager use?
- Pareto chart
- Fishbone diagram (cause and effect diagram)
- Control chart
- Scatter diagram
Correct Answer: B — Fishbone diagram (cause and effect diagram)
Explanation: A fishbone diagram is used to brainstorm and organize possible causes of a problem by category before validating them with data.