Score your 5 Why root cause analysis by depth and evidence strength. Determine if your investigation reaches actionable root causes.
5 Why analysis is a root cause investigation technique where you ask "Why?" iteratively (typically five times) to drill past symptoms to the true root cause. While simple in concept, the quality of a 5 Why analysis varies significantly depending on how deep the investigation goes and how well each answer is supported by evidence.
This calculator scores a 5 Why analysis on two dimensions: depth (how many meaningful "why" levels were explored, 1–5) and evidence strength (how well each level is supported by data, 1–3 scale). The combined score indicates whether the analysis is likely to reach an actionable root cause.
A high score suggests the analysis reached a genuine root cause with strong supporting evidence. A low score suggests the investigation stopped too early or relied on assumptions rather than verified facts.
Integrating this calculation into regular operational reviews ensures that key decisions are grounded in current data rather than outdated assumptions or rough approximations from the past.
Not all 5 Why analyses are equal. Scoring the analysis forces teams to evaluate whether they dug deep enough and gathered sufficient evidence, preventing shallow investigations that address symptoms instead of root causes. Precise quantification supports benchmarking against industry standards and internal targets, driving accountability and continuous improvement throughout the organization.
Score = Depth (1–5) × Average Evidence Strength (1–3) Score range: 1 to 15 Actionability: • Score ≥ 10 — Actionable root cause likely found • Score 6–9 — Potentially actionable, consider deepening • Score < 6 — Likely still at symptom level
Result: Score = 10.0 — Actionable
The analysis reached 4 levels of "Why" with an average evidence strength of 2.5 (between observation and verified data). Score = 4 × 2.5 = 10. This indicates the team likely found an actionable root cause.
The 5 Why technique originated in the Toyota Production System. Taiichi Ohno emphasized that by asking "Why?" repeatedly, engineers could move from obvious symptoms to the true root cause, enabling permanent corrective actions rather than temporary fixes.
Use a fishbone (Ishikawa) diagram to brainstorm potential causes across categories (Man, Machine, Method, Material, Measurement, Environment). Then apply 5 Why to the most likely causes identified in the fishbone to drill down to root causes.
High-quality 5 Why analysis requires data at each level. Go to the gemba (the actual place), observe the process, review records, and verify each answer before proceeding to the next "Why." Assumptions lead to incorrect root causes and ineffective corrective actions.
Five is a guideline, not a rule. Taiichi Ohno (Toyota) observed that asking "Why?" five times typically reaches a root cause. Sometimes three is enough; sometimes more are needed. Stop when you reach a cause you can act on.
Level 1 (assumption): "We think it's because..." Level 2 (observation): "The operator noticed..." Level 3 (verified data): "Data from the log shows..." Aim for level 2–3 at every level.
For complex problems with multiple contributing causes, 5 Why may be too simplistic. Consider combining it with fishbone diagrams (to identify branches) and then running 5 Why on each significant branch.
Stopping too early (e.g., "operator error" at level 2) is the most common mistake. Always ask why the error was possible — this leads to systemic improvements like error-proofing and procedure changes.
Focus on process, not people. Instead of "Why did the operator make a mistake?", ask "Why did the process allow the mistake?" or "Why wasn't there a detection mechanism?" This leads to systemic solutions.
Yes. Document the problem statement, each why level and answer, evidence citations, root cause, and corrective actions. This creates a knowledge base and demonstrates due diligence in investigations.