Originally posted on Quality Progress by Vidyasagar A

Root cause analysis reminds me of the intriguing mind of a child: Both use common questions that start with “what,” “how” or “why” in an attempt to understand something and uncover answers.

Children often satisfy their curiosity as they ask questions to better understand their environment. You could say that they’re already unknowingly using a simple, yet essential quality tool-five whys analysis-to clarify their own questions and get to the truth.

If five whys analysis is used in science to achieve a clear objective, the tool can be just as powerful in the business world as it is for children exploring their own surroundings. As a practicing Master Back Belt, I often use this technique to successfully arrive at the root causes of problems.

What’s five whys analysis?
Five whys analysis is the art of systematically drilling down to a real root cause (see Figure 1). It’s a simple, yet effective way to determine the root causes in almost any situation. Essentially, you can find the root cause of a problem and show the relationship of causes by repeatedly asking the question, “Why?”

Does this remind you of the lean tool TRIZ, or the theory of inventive problem solving? It should, because they can complement each other well.

Online Figure 1 shows a simple example of five whys analysis of “Getting caught speeding on the road.” This particular example captures just one answer for every why question asked. Typically, you would have more than one answer for every why question, and each one could be subjected to another why question


Applying five whys analysis
You could say five whys analysis is the art of asking the right question at the right time. In Online Figure 1, it’s important not to skip levels of questions or hurry through them to reach a perceived root cause. You must approach this analysis step by step with logical questions summarizing the observations from earlier questions.


Don’t get too caught up with asking five questions. Sometimes, it may take just three why questions to reach the root cause. Other times, it might take many more. Once, I had to ask 14 whys to reach a root cause. As you master the art of questioning, you will arrive at the root cause much more quickly.

Things to remember
It’s important not to leave any loose ends. Each loose end must be tied up with a fresh why question, or it should become part of another question being asked.

Another critical point in this analysis is knowing when to stop asking why. Some experienced practitioners say that you have reached the true root cause when the answer to your why question is a process, policy or a person. Often, these answers turn out to be the real root causes.

Knowing when to stop mostly depends on three questions:

  1. How relevant are the questions and answers to the original X or Y you are investigating?
  2. Did you find a root cause that helps you control or avoid the situation?
  3. Are the questions and answers significant enough, considering your project scope?

The real problem
When and where to stop questioning why is the most important part of this approach: Do not stop unless you reach a process, policy or a person that seems to be a root cause. Often, there can be many root causes with a compounding impact placed at different stages of the five whys drill-down.

It is also important to recognize that the real problem in a Six Sigma project is not that we don’t know the solutions. The real problem is that we don’t know real root causes.

Often, some X’s might not have further data to further drill down using Six Sigma tools. Hence, using five whys analysis is almost essential in Six Sigma implementation. Correctly using this technique can be a big differentiator for the project.

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