5 Whys


The ‘root cause’ is the true or underlying reason why something has happened – usually something that has gone wrong. Finding the root cause enables appropriate action to be taken to prevent a problem from happening again—for example, when a nonconformity report (NCR) is raised. Otherwise, action taken may be focussed on the effect rather than the true cause. Therefore, when undertaking investigations into an incident (whether quality or otherwise), specific attention is given to identifying the root cause.

The ‘5 Whys’ is a very simple but effective way to help determine the root cause of an issue by continually asking ‘why’ until the root cause is identified.

What is 5 Why’s?

It is not unusual for young children to ask ‘why’ when discussing something. Having been given an answer by the adult, the young child then asks ‘why’ again but this time in relation to the answer given, the adult answers and the child persists asking why again in relation to the next answer and so on. This can be very annoying! However, the child is actually demonstrating the principles of the ‘5 Whys’ very effectively. The child (perhaps unknowingly) is trying to find the basis of the reason for the adult’s decision.

The ‘5 whys’ quality tool is simply a way to delve deeper and deeper into the reasons for what has happened. Each time a question is asked and answered we can refer to this as a ‘level’. When no further answers can be given, theoretically, the ‘root cause’ has been determined.

It is often assumed that asking ‘why’ 5 times allows the root cause to be identified (although this may not always be the case).

  Question Answer
Level 1 Why was the bolt not tightened to the correct torque? The operative was not aware that the bolt had to be tightened to a specified torque.
Level 2 Why was the operative not aware that the bolt had to be tightened? The operative did not receive information from the supervisor.
Level 3 Why did the supervisor not supply information to the operative? The supervisor did not have the information available.
Level 4 Why did the supervisor not have the information available? The supervisor could not access the network drive system.
Level 5 (root cause) Why could the supervisor not access the network drive system? There was no power due to electrical testing.


It is important to recognise that an issue may initially appear to be the result of one thing when actually the root cause is very different. It is the root cause that will enable the problem to be solved and prevent it from happening again.

A form to help use the 5 Whys quality tool can be downloaded here.


Original article written by Mike Buss, reviewed by Tony Hoyle on behalf of the CQI Construction Special Interest Group, and accepted for publication by the Competency Working Group on 7 March 2018.

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