5 Whys 3‑Legged 5 Whys
Run all three legs from the same problem. Entries auto-save in this browser. Use Save as PDF for a watermarked copy.
Vanguard Quality Partners
Root-Cause Analysis Toolkit
3‑Legged 5 Whys
Vanguard Quality Partners
Defects Out. Confidence In.
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Problem / Project
Owner / Team
Date
Reference #
Problem StatementOne problem, investigated three ways.
Leg 1
Occurrence
Why did it happen?
The specific, direct cause — why the defect was made.
1
Why?
2
Why did that happen?
3
Why did that happen?
4
Why did that happen?
5
Why did that happen?
Root Cause — Occurrence
Leg 2
Detection
Why did it escape?
Why our checks and controls did not catch it first.
1
Why?
2
Why did that happen?
3
Why did that happen?
4
Why did that happen?
5
Why did that happen?
Root Cause — Detection
Leg 3
Systemic
Why did the system allow it?
Why the process or management system permitted the gap.
1
Why?
2
Why did that happen?
3
Why did that happen?
4
Why did that happen?
5
Why did that happen?
Root Cause — Systemic
Corrective & Preventive Action
Action(s) — make / detect / system
Owner
Due Date
Verification of Effectiveness
How to use the three legs

Occurrence asks why the defect was created. Detection asks why it slipped past your controls. Systemic asks why the process or management system allowed the gap. Drive each leg to a process-level root cause, then close all three with one corrective-action plan — that's how a fix actually holds.

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