5-Whys
Definition
An iterative questioning technique that moves from a symptom to underlying causes by asking 'why?' repeatedly until a systemic explanation is reached.
- Type
- Iterative questioning technique
- Field
- Root-cause analysis
- Method
- Repeatedly ask why until a systemic cause emerges
Common questions
What is the main weakness of the 5-Whys method?+
It follows a single linear chain of causation, so it can miss situations where an incident actually has several contributing causes acting together, rather than one root cause reachable by asking why repeatedly.
Is 5-Whys normally used on its own in an investigation?+
It is often paired with a more structured tool, such as a fishbone diagram or a fault tree, so that the branching factors a single why-chain would miss still get captured and organised.
Related terms
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- Fault Tree Analysis (FTA)
- A top-down, deductive Boolean logic model that works backward from a specific undesired top event through AND/OR gates to identify minimal cut...
- FMEA / FMECA
- Failure Mode and Effects Analysis is a bottom-up, inductive method listing what can fail in each component and the effect on the...
- Minimal Cut Set
- In a fault tree, the smallest set of simultaneously failing basic events that is sufficient to cause the top event. Identifies the...
- Root Cause
- The fundamental, underlying deficiency from which the failure originated. Distinguished from immediate cause (the final physical event) and contributing factors. Root-cause analysis...