Five why "nots": Using more than the "5 whys" method for root cause analysis

Using 5 Whys alone may leave engineers with an incomplete root cause picture, which is why other methods should be considered to help solve the problems and keep them from recurring.


Photo by William Iven on UnsplashFirst of all, it is important to understand what 5 Whys is before exploring what it is not. It is a problem solving tool used in many facilities and is commonly associated with Lean, Six Sigma and Kaizen implementations. The technique was originally developed by Sakichi Toyoda and was used within the Toyota Motor Corporation during the evolution of its manufacturing methodologies. The method is quite simple really and involves asking "why" multiple times until the individual believes that they have reached the process cause of the problem. This sometimes (but not always) means you will stop at the fifth "why" hence the name.

While 5 Whys may be a great problem solving tool, it is not a great root cause analysis (RCA) tool for five reasons:

1. There really is no such thing as "root cause." A more correct phrase would be "root causes” because there are almost always conditions and actions that come together to manifest the failure. 5 Whys as it is most often used only addresses one branch of the causal chain either the condition or the action.

2. By only following one causal chain, you do not get the opportunity to analyze all the contributing causes and look for the lowest cost solution that eliminates or mitigates the risk to an acceptable level.

3. The results from 5 Whys are not repeatable. Different people using 5 Whys come up with different causes for the same problem. It is all based on their existing knowledge and experience.

4. Many times, 5 Whys is just used to prove what the practitioner already thought instead of looking at other possibilities. 5 Whys investigators are plagued by an inability to go beyond their current knowledge which leads to them not identifying causes that they do not already know.

5. Engineers that use 5 Whys alone do more investigations due to problem recurrence. They are sometimes celebrated for their ability to do 27 RCA investigations per month. However, when you look at the list, 18 are problems that they should have taken the time to do a true analysis the first time and they would not be focusing on them again. Using the 5 Whys method causes a tendency for investigators to stop at symptoms rather than going on to lower-level root causes, which leads to the problem recurring.

Shon Isenhour is a founding partner at Eruditio and is a part of Plant Engineering's editorial advisory board. Eruditio is a CFE Media content partner. This article originally appeared on Eruditio's blog.

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