5 Why Root-Cause Analysis
Build an evidence-based cause chain from a precisely defined problem to a controllable process cause and corresponding corrective action.
Purpose and method
Explore cause-and-effect chains by repeatedly asking why and marking the verified root-cause candidate.
When to use it
Use 5 Why for focused problems where evidence can progressively connect the symptom to a controllable cause.
Core principle
The number five is a prompt, not a rule. Stop when the cause is verified, actionable at the appropriate system level and explains the observed problem.
What the interactive module provides
- Cause chain
- Evidence notes
- Root-cause candidate
- validated cause chain, root-cause statement and linked corrective actions
Professional verification: The module supports learning, analysis and documentation. Verify results against actual process conditions, internal standards, safety requirements and competent professional judgement before implementation.
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Recommended workflow
Build an evidence-based cause chain from a precisely defined problem to a controllable process cause and corresponding corrective action.
- 1
Define one observable problem without embedding a cause
- 2
Ask why it occurred and collect supporting evidence
- 3
Repeat from the verified answer, not from an assumption
- 4
Test whether the final cause predicts the problem
- 5
Assign containment, corrective action and verification
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Practical example
A sensor fails to detect a part because its bracket moved; the bracket moved because the clamp had no defined torque; torque was undefined because the maintenance standard omitted the joint.
Calculation or verification principle
No fixed calculation applies. For every “why”, record the evidence that proves the causal link and whether an alternative cause remains possible.
Required inputs → Expected outputs
- Required inputs
- specific problem statement, time and place, observations, records, tests and responsible process owner
- Expected outputs
- validated cause chain, root-cause statement and linked corrective actions
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Common mistakes to avoid
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Writing “operator error” as the root cause
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Forcing exactly five levels
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Mixing several causal branches into one chain
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Accepting plausible wording without verification
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Frequently asked questions
What data do I need to use this tool?
Prepare specific problem statement, time and place, observations, records, tests and responsible process owner.
What result does the module produce?
The module produces validated cause chain, root-cause statement and linked corrective actions.
Can I implement the result without further review?
No. Treat the output as a structured engineering and improvement aid. Verify source data, assumptions, safety, quality, legal requirements and local process conditions with competent responsible people before implementation.
LEAN Toolbox
Open interactive tool →5 Why Root-Cause Analysis
Build an evidence-based cause chain from a precisely defined problem to a controllable process cause and corresponding corrective action.