Cause-and-Effect Diagram

PMBOK v8 Definition

A cause-and-effect diagram is a visual representation that helps trace an effect back to its root cause. This diagram may also be known as a fishbone or Ishikawa diagram. It breaks down the causes of the problem statement identified into discrete branches, helping to identify the main or root cause of the problem.

Why It Matters for the Exam

The cause-and-effect diagram appears frequently in PMI exam questions related to quality management and root cause analysis. You will encounter it in situational questions where a project team needs to identify why a defect occurred or why a process is failing, requiring you to select the appropriate tool for systematic cause investigation.

Key Points to Remember (for the exam)

• Primary Purpose: Trace an effect back to its root cause by breaking down causes into discrete branches
• Alternative Names: Also known as fishbone diagram or Ishikawa diagram
• Key Input: A clearly defined problem statement (the "effect" or "head" of the fish)
• Core Technique: Decompose causes into discrete branches to systematically identify main or root causes
• Common Confusion: Not used for prioritizing causes (use Pareto diagram for that); it identifies possible causes, not their frequency or impact
• Typical Application: Quality management processes, particularly in Plan Quality Management and Manage Quality
• Visual Structure: Resembles a fish skeleton, with the problem at the head and causes branching off the spine

Typical PMI Exam Example

A project team is experiencing recurring defects in software deliverables. The project manager facilitates a session where team members brainstorm potential causes, organizing them into categories such as people, processes, technology, and environment. The team traces each branch to identify the root cause of the defects. Which tool is being used? → The cause-and-effect diagram.

PMI Exam Traps

• Trap: Confusing cause-and-effect diagram with a flow chart

  • Reality: A flow chart shows sequence of steps; a cause-and-effect diagram shows cause relationships branching from a problem

• Trap: Thinking the diagram provides quantitative data on cause frequency

  • Reality: It identifies possible causes qualitatively; use Pareto charts or histograms for quantitative prioritization

• Trap: Assuming it is only used in predictive (waterfall) projects

  • Reality: It is used in any project type where root cause analysis is needed, including adaptive approaches

• Trap: Confusing it with a burndown chart or burnup chart

  • Reality: Burndown/burnup charts track work completed/remaining over time; cause-and-effect diagrams trace causes of a problem

Important PMI Connections

Quick Review Questions

1. A project team is investigating why a manufacturing process produces 15% defective units. They draw a diagram with the problem at the head and causes branching into categories like materials, methods, and machinery. What is this diagram called?

2. What are the three alternative names for a cause-and-effect diagram in PMBOK v8?

3. A PMP candidate confuses a cause-and-effect diagram with a tool that shows work remaining over time. Which chart tracks work completed toward a milestone and is used mostly within adaptive development approaches?

4. During which quality management process would a project team most likely use a cause-and-effect diagram to analyze defects?

5. What is the key difference between a cause-and-effect diagram and a Pareto diagram in quality problem-solving?

PMBOK v8 Reference

Section 5.2.2.3 - Cause-and-Effect Diagram (Fishbone/Ishikawa)
Section 5.2.2.4 - Burnup Chart (related visual tool for comparison)