“5 Why” Tool – Pros & Cons

5-why is one of the principal root cause analysis tools in manufacturing. The idea is to iteratively asking “why”. Answer of each “why” becomes the question for the next “why”.

This method was developed by Sakichi Toyoda, in his textile company and is about 100 years old! The idea is to find the source of a failure and implement controls to prevent the problem from happening again.

Although its widespread use, 5-why comes with some drawbacks that could prevent one from reaching the true root cause of a problem. First off, there usually more than one root cause to a problem. These are categorized in manufacturing as Prevention Causes, Detection Causes and Systematic Causes. This means we need to use 5-why method multiple times with a different sequence each time. The line of question is not defined with this method, meaning depending on experience and persistence of the person utilizing the method, different causes will emerge.

On the other hand, to overcome these shortcomings, 5-why is usually used along with other methods such as fishbone diagram. The idea is to explore various routes a failure could be created.

Another issue with 5-why is that people involved in the problem solving usually tend to stop at more superficial causes rather than the true cause. This is often linked to the investigator’s knowledge on the failure topic. Therefore, 5-why tool must be used by experts in the domain of the problem.

At the end of the day, to validate any root cause, one must remember that the cause has to be repeatable. Simulation of the root cause is key and that is reason behind utilizing 5-why with methods like fishbone or tabular format.

To review this 5-why method, we have put together a guide which is available here.

Thanks and keep practicing!

Kinemative