Cause and Effect Diagrams for PMPs: Fishbone Examples, Steps, and Exam Tips
A cause and effect diagram is a quality tool that maps every possible cause of a problem onto a fish-skeleton chart so a team can find the root cause. It is 1 of the 7 basic quality tools. Kaoru Ishikawa developed it in the 1960s, which is why it is also called the Ishikawa or fishbone diagram.
The PMP exam tests the tool by name, by synonym, and by category. This article defines the diagram, labels its 3 parts, lists the 6M categories, walks through 5 creation steps with a worked example, and shows how the diagram pairs with the 5 Whys and the Pareto chart.
What is a cause and effect diagram?
A cause and effect diagram is a visual tool that organizes the potential causes of 1 problem into categories. The problem sits at the head, the spine carries the categories, and the bones carry the causes. Teams use it to separate root causes from symptoms.
The tool has 5 names that appear on exams: cause-and-effect diagram, fishbone diagram, Ishikawa diagram, Fishikawa diagram, and herringbone diagram. All 5 describe the same chart.
The diagram has 3 parts:
- Head: the effect, which is the problem stated in 1 clear sentence.
- Spine: the horizontal line that connects the categories to the head.
- Bones: the branches that group causes by category, with sub-branches for deeper causes.
Ishikawa used the chart for quality control at Kawasaki shipyards in Japan. Project teams now use it on defects, delays, cost overruns, and process failures.
Where does the cause and effect diagram fit in the PMBOK Guide?
The cause and effect diagram is 1 of the 7 basic quality tools. PMBOK Guide 6th Edition lists it as a data representation technique in the Manage Quality and Control Quality processes. It also supports root cause analysis on risks and problems.
The 7 basic quality tools are:
| Tool | Purpose |
|---|---|
| Cause-and-effect diagram | Maps possible causes of a problem |
| Flowchart | Shows how process steps connect |
| Checksheet | Tallies data on quality problems |
| Pareto diagram | Ranks problems by frequency |
| Histogram | Shows the distribution of data |
| Control chart | Tracks process stability against control limits |
| Scatter diagram | Tests whether 2 variables are related |
The Plan Quality Management process decides which tools the team uses. Control Quality applies them to measurements and results. The tool works in predictive, hybrid, and agile projects. In agile work, teams use it during retrospectives to trace a recurring impediment.
What categories does a cause and effect diagram use?
The most common categories are the 6Ms: manpower, machine, method, material, measurement, and mother nature (environment). Service projects use 4Ss: skills, suppliers, surroundings, and systems. Marketing and service organizations use up to 8Ps.
| Category set | Categories | Typical setting |
|---|---|---|
| 4Ms (basic) | Methods, machine, materials, measurements | Manufacturing |
| 6Ms | Manpower, machine, method, material, measurement, mother nature | Manufacturing and general projects |
| 4Ss | Skills, suppliers, surroundings, systems | Service and support |
| 8Ps | Price, people, product, procedure, promotion, policy, place, processes | Service organizations and marketing |
A diagram can carry more than 4 categories. Teams also invent categories that fit the problem, such as vendor, policy, or technical expertise.
How do you create a cause and effect diagram?
Create the diagram in 5 steps: define the problem, draw the backbone and categories, brainstorm causes, analyze each cause, and draw the final chart. Step 4 takes the most time and decides the quality of the result.
Follow these 5 steps:
- Define the problem in 1 specific sentence and get stakeholder agreement.
- Draw the spine, the head, and 1 bone per category.
- Brainstorm causes with the team and place each under its category.
- Analyze each cause by asking why it happens, then mark the most probable causes.
- Finalize the chart on a whiteboard, a shared canvas, or software.
Three conditions produce reliable results: the team knows the problem in depth, the project manager facilitates to keep discussion on topic, and the team works from facts instead of opinions.
What is an example of a cause and effect diagram?
A worked example traces 1 problem, “release defects exceed target,” through the 6M categories. Each bone lists the contributing causes. The team then selects the most probable causes for verification with data.
This illustrative software project example uses the 6Ms:
| Category | Contributing causes |
|---|---|
| Manpower | New developers without code review training; QA understaffed in release week |
| Machine | Test environment differs from production; outdated build server |
| Method | No regression test before release; unclear definition of done |
| Material | Incomplete requirements; stale test data |
| Measurement | Defect counts not tracked by module; no code coverage metric |
| Mother nature (environment) | Compressed deadline set by a client contract; remote team across 3 time zones |
The head of the diagram reads “Release defects exceed target.” The team marks 3 probable causes: missing regression tests, a test environment mismatch, and a compressed deadline. It then collects defect data to confirm which cause produces the most defects.
How does a cause and effect diagram work with the 5 Whys and the Pareto chart?
The fishbone finds the possible causes, the Pareto chart ranks them by frequency, and the 5 Whys drills from a chosen cause to its root. The 3 tools run in sequence: map, prioritize, drill.
- Fishbone first: it lists every candidate cause so the team does not stop at the obvious one.
- Pareto chart next: it ranks causes by frequency or impact when counts exist, so the team attacks the largest first.
- 5 Whys last: it asks “why” repeatedly on the top cause until the root cause appears. The 5 Whys typically yields 1 root cause per chain.
Other complements include the scatter diagram, which tests whether a suspected cause and the effect move together, and failure mode and effects analysis (FMEA), which uses fishbone output to list failure modes. Teams that group brainstormed causes in a workshop often pair the fishbone with affinity diagrams.
What are the advantages and limitations of cause and effect diagrams?
The diagram has 4 advantages: it forces a complete search for causes, it makes complexity visible, it costs almost nothing, and it builds shared understanding. It has 3 limitations: opinion-driven input, clutter on large problems, and no ranking of causes.
Advantages:
- Complete search: the categories push the team past the obvious cause.
- Visible complexity: a multi-cause problem fits on 1 page.
- Low cost: a whiteboard or free template is enough.
- Shared understanding: the chart records which causes the team explored.
Limitations:
- Opinion over fact: unverified guesses produce wrong corrective actions.
- Clutter: large problems create dense charts that lose readability.
- No ranking: the chart lists causes but does not weight them, so the team adds a Pareto chart.
A quality management plan states when the team applies the tool. Study how to document those decisions in the quality management plan guide.
How does the PMP exam test cause and effect diagrams?
The exam tests 4 skills: recognizing the 5 synonyms, classifying causes into categories, choosing the tool for a scenario, and sequencing it with the Pareto chart and 5 Whys. Scenario questions describe a recurring defect and ask for the best next step.
Prepare with these 5 actions:
- Memorize the 5 names: cause-and-effect, fishbone, Ishikawa, Fishikawa, herringbone.
- Recall the 6Ms and classify sample causes into them.
- Identify the tool when a question describes finding all possible causes of a defect.
- Sequence the quality tools: fishbone to list causes, Pareto to rank, 5 Whys to reach the root.
- Separate the cause and effect diagram from the flowchart, which shows process steps, and the control chart, which shows stability over time.
The 2026 PMP exam places about 60% of questions in agile and hybrid contexts. Quality tool questions appear in those scenarios too. Build recall with the PMP course materials from Project Management Training Institute, which cover the 7 basic quality tools in exam context.
