The 5 Whys is a simple but powerful technique for finding the root cause of a problem.
There are no real rules for performing a 5 Whys analysis. Simply state the problem which has occurred and ask “why” until you exhaust all reasoning, at this point your have likely found the root cause. This normally occurs within 5 asks of “Why?” but you should ask it as many or as few times as needed.
You will sometimes find that there are multiple reasons why something might have happened. In this case you should pursue each line of enquiry with its own series of whys, a Fishbone diagram may help you keep track of that.
Problem: The car would not start.
- Why? – The battery is dead. (First why)
- Why? – The alternator is not functioning. (Second why)
- Why? – The alternator belt has broken. (Third why)
- Why? – The alternator belt was well beyond its useful service life and not replaced. (Fourth why)
- Why? – The vehicle was not maintained according to the recommended service schedule. (Fifth why, a root cause)
During my research for this post I came across the following recommendations for performing a 5 Whys workshop.
- It is necessary to engage the management in the five whys process in the company. For the analysis itself, consider what is the right working group. Also consider bringing in a facilitator for more difficult topics.
- Use paper or whiteboard instead of computers.
- Write down the problem and make sure that all people understand it.
- Distinguish causes from symptoms.
- Pay attention to the logic of cause-and-effect relationship.
- Make sure that root causes certainly led to the mistake by reversing the sentences created as a result of the analysis with the use of the expression “and therefore”.
- Try to make answers more precise.
- Look for the cause step by step. Don’t jump to conclusions.
- Base our statements on facts and knowledge.
- Assess the process, not people.
- Never leave “human error”, “worker’s inattention”, “blame John”, etc. as the root cause.
- Foster an atmosphere of trust and sincerity.
- Ask the question “Why?” until the root cause is determined, i.e. the cause the elimination of which will prevent the error from occurring again.
- When you form the answer to the question “Why?” it should be from the customer’s point of view.
This approach is credited to Japanese inventor and founder of the Toyota company Sakichi Toyoda (1869-1930). It has continued to be used at the company right up until present day. It is reportedly taught as part of the induction to the Toyota Production System which many Lean concepts are based upon.