Root cause analysis is the systematic work of identifying the actual source of a nonconformity or problem rather than its visible symptoms.
Its purpose is to ensure that corrective action is applied at the right point. A wrongly identified root cause results in the problem recurring despite the resources spent.
Common methods
- 5 Whys: Drilling from symptom to source with successive “why” questions
- Fishbone (Ishikawa): Grouping causes under people, machine, material, method, measurement and environment
- Fault tree analysis: Breaking down the possible causes of an event in a logical structure
- 8D: The team-based eight-step problem-solving approach widely used in automotive
Three common mistakes
Stopping at the person. “Operator error” is not a root cause. The question is why the operator was able to make the error: training, instructions, ergonomics, workload, lack of error proofing.
The auditor writing it. Root cause analysis is the responsibility of the audited department. The auditor identifies the finding; finding the cause is the process owner’s job.
Reducing it to a single cause. Most problems have more than one contributing cause. In addition, “why was it not detected” should be asked as much as “why did it occur.”
Root cause analysis is the common ground of both management system and automotive problem-solving approaches. It is addressed in the context of audit findings in the ISO 19011 training; for 8D and structured problem-solving methods in automotive, see our Core Tools and CQI programmes.