The 5 Whys is a basic root cause analysis technique used in the Analyze phase of the Six Sigma DMAIC (Define, Measure, Analyze, Improve, Control). To solve a problem, we need to identify the root cause and then eliminating it. Therefore, main goal of the is to drill down to the bottom of problem to find out problem of occurrence or root cause and thereby preventing its recurrence.

It might be that child’s favorite technique to ask “Why” to her dad which makes her dad crazy, but this is teaching us an important Six Sigma Quality chapter.

5 Whys is a simple technique which does not contain hypothesis testing, regression analysis, data segmentation or other types of advanced statistical tools. Here its is simple as we ask “Why” until we can’t ask “Why” again. 5 is a good rule of thumpb (of course arbitrary) and by often querying “Why”, we can quickly reach at the underlying causes of a problem.


Sakichi Toyoda, one of the fathers of the Japanese industrial revolution and the founder of Toyota Industries Corporation developed this technique in the 1930s. By 1970s, this method became popular and Toyota and many other firms are still using this it to solve problems.

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How to Complete the 5 Whys

Step 1. Forming a team:

Here the team members who gathered should be the ones familiar with details, affected or noticed the problem.

After this, select a master for the meeting who is going to lead the discussion, ask the 5 whys, and assign responsibility for the solutions the group comes up with.

Step 2. Define the Problem:

After observing the problem, write down a clear problem statement which is acceptable by all team members.

Step 3. Ask the “Whys for 5 times?”:

Answer at least five levels of “whys.” This seems to be easy but some times it turns to be the difficult part. The key part in this step is to start with right question. There are two types of approach which can be adapted in this step by the team such as single lane 5 Whys or multiple lane 5 Whys.

Single Lane Process

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Multi-Lane Process

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Step 4: Addressing root cause and assigning responsibilities:

After identifying true root cause of the problem, the team need to discuss and agree the practical as well most effective counter measures that fits for their case to prevent the recurrence of the problem.

Step 5. Monitor the measures:

Continue monitoring the counter-measures until the problem statement is eliminated effectively or completely. Repeat the steps of 5 Whys if necessary to ensure that you’ve identified the correct root cause.

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Limitations of the 5 Whys

5 whys will not help us in root cause analysis if the cause is unknown. That is, we cannot reach to counter measure if the person or team doing this type of analysis doesn’t know the problem or couldn’t provide meaningful answers to the questions. Sometimes assumptions that we take in each step might not be the real underlying cause of the problem there may be more causes to the problem. Also 5 Whys have clear inability to differentiate between causal factors and root causes, and the lack of rigor where users aren’t required to test for sufficiency the root causes generated by the method. The success of this method is completely depending to degree upon the skill with which the method is applied.

5 Whys make use of counter measures approach than giving priority to solution approach. In counter-measure which is robust method, a set of actions are taken to prevent the reappearance of root cause problem but in the case of solution approach, we have to give priority to symptom by finding out the real solution for the root cause rather than preventing it from recurring.

In industries such as nuclear, health care, aviation, and aerospace, 5 Whys are inadequate for problem solving and need more advanced root cause analysis techniques.

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