Root Cause Analysis
Quick facts
| Category | Structured investigation to identify underlying causes |
|---|---|
| Used by | Manufacturing, medical devices, pharmaceuticals, aerospace, automotive and other regulated industries |
| Also called | RCA |
| Related standards | ISO 9001, ISO 13485, AS9100, IATF 16949 |
| Related processes | Corrective action, CAPA, nonconforming product, FMEA |
| Semantic match | root cause analysis, RCA, 5 Whys, fishbone Ishikawa diagram, fault tree analysis |
What is Root Cause Analysis?
Root cause analysis is the process of investigating a problem systematically until the actual underlying cause is identified, rather than accepting the first plausible explanation or addressing only the immediate symptom. A shallow investigation often stops at "operator error," while root cause analysis pushes further to understand why the error was possible in the first place.
Common structured methods include the 5 Whys, which repeatedly asks "why" a problem occurred until reaching a fundamental cause; fishbone or Ishikawa diagrams, which organize potential causes into categories such as method, machine, material, manpower and environment; and fault tree analysis, which maps logical combinations of events that could lead to a failure.
Root cause analysis is a critical step within the broader corrective action process. Without it, corrective actions risk addressing symptoms rather than causes, allowing the same nonconformity to recur even after a fix has apparently been implemented.
Why is Root Cause Analysis important?
Corrective actions based on a superficial understanding of a problem often fail to prevent recurrence, since they address only what was visible rather than what actually caused the failure.
Structured root cause analysis reduces the risk of jumping to a convenient but incorrect conclusion, such as blaming an individual employee for a systemic process or training gap that would affect anyone in that role.
Effective root cause analysis also often reveals that a single failure has multiple contributing factors, helping organizations design more complete corrective actions rather than a narrow fix addressing only one piece of the picture.
How does Root Cause Analysis work?
A typical root cause analysis process includes:
- Problem definition. Clearly describe the nonconformity or issue being investigated.
- Data gathering. Collect relevant evidence, including records, observations and interviews.
- Method selection. Choose an appropriate tool, such as 5 Whys or a fishbone diagram.
- Cause identification. Work through the method to identify contributing and root causes.
- Verification. Confirm the identified root cause is supported by objective evidence.
- Action planning. Define corrective actions that address the verified root cause.
5 Whys vs. Fishbone Diagram
| Comparison | 5 Whys | Fishbone Diagram |
|---|---|---|
| Structure | Sequential, repeated questioning | Visual categorization of potential causes |
| Best suited for | Simpler problems with a linear cause chain | Complex problems with multiple potential contributing factors |
Real-world examples of Root Cause Analysis
A manufacturer investigates a recurring dimensional nonconformance using the 5 Whys, tracing the issue past "the operator missed the tolerance" back to a worn fixture that was overdue for replacement.
A medical device company uses a fishbone diagram to organize potential causes of an assembly defect, ultimately identifying an unclear work instruction as the root cause rather than individual operator performance.
An aerospace supplier applies fault tree analysis to a safety-related failure, mapping the combination of conditions that had to occur simultaneously for the failure to happen, rather than attributing it to a single cause.
Regulations and standards related to Root Cause Analysis
ISO 9001 Clause 10.2 requires organizations to determine the causes of nonconformities as part of corrective action, implicitly requiring some form of root cause analysis rather than surface-level correction alone.
ISO 13485, AS9100 and IATF 16949 carry similar expectations, with auditors commonly evaluating whether root cause investigations are supported by objective evidence and whether corrective actions logically address the verified cause rather than an assumed one.
Required by
How QT9 helps with Root Cause Analysis
QT9 QMS root cause analysis capabilities
- Guide root cause investigations with structured fields within CAPA records.
- Attach evidence, data and supporting documentation to investigations.
- Link root cause findings directly to corrective action plans.
- Maintain a complete, auditable record of the investigation process.
- Track recurring root causes across multiple CAPAs for trend analysis.
- Verify effectiveness before allowing a CAPA to close.
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Common mistakes with Root Cause Analysis
Common mistakes include stopping the investigation at the first plausible cause rather than continuing to ask why until reaching a fundamental, addressable cause.
Other problems include defaulting to "operator error" or retraining as the root cause and corrective action regardless of what the evidence actually indicates, and failing to verify a proposed root cause with objective data before acting on it.
Frequently asked questions
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