Definition
Root Cause Analysis (RCA) is a structured investigation used to explain why an unwanted event, failure or recurring problem occurred and to identify controllable conditions whose removal or modification can reduce recurrence.
Purpose and Conditions of Use
RCA is appropriate when the event matters, the causal explanation is uncertain and action should address more than the visible symptom. The problem, scope, evidence requirements and decision owner should be defined before selecting a technique.
Analytical Process
- Define the event, impact, boundary and expected condition.
- Preserve and collect records, observations, measurements and physical evidence.
- Reconstruct the sequence and distinguish facts from assumptions.
- Develop plausible causal paths, including technical, organisational and human conditions.
- Test each claim against evidence and competing explanations.
- Select actions that control verified causes and define how effectiveness will be checked.
Evidence Standard
A cause should explain the observed event, be supported by available evidence and remain credible when alternative explanations are considered. Correlation, timing or repetition alone does not prove causation.
The strength of the conclusion must not exceed the strength of the evidence.
Supporting Methods
Depending on the event and evidence, RCA may use Five Whys, cause-and-effect diagrams, fault trees, event timelines, change analysis, barrier analysis, process mapping, statistical analysis or testing. These tools support reasoning; none of them is RCA by itself.
Common Failure Modes
- Stopping at the first plausible explanation.
- Confusing a human action with a complete causal explanation.
- Using a preferred tool before defining the problem.
- Relying on opinion while evidence remains available.
- Choosing retraining or a new procedure as the default action.
- Closing the investigation without verifying action effectiveness.
Method Boundary
RCA does not guarantee one single root cause. Complex events commonly involve several interacting causal and contributing conditions. The method does not replace immediate containment, risk control or specialist safety investigation.
The objective is not to find the deepest possible cause, but the most useful verified cause that can support effective decision-making.
Practical Perspective
The objective of RCA is not to identify someone to blame. Its objective is to understand why the system allowed the event to occur and which changes are most likely to reduce recurrence.