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5 Whys

5 Whys

5 Whys is one of the common techniques for problem-solving and root cause analysis. It is also one of the simplest techniques and easiest to put into practice. It is used in everyday business situations to identify the possible causes underlying a specific problem. It was introduced and made popular by Toyota as part of their Toyota Production System, and it is now widely used within Lean and Six Sigma frameworks.

5 Whys is one of the cause-and-effect analysis tools that helps to identify the possible sources of variation in a process. Yet, it is so simple that can be implemented without collecting data and without the need for advanced statistical techniques. It only requires to ask, “Why does this happen?” several times over a problem, waste or defect. The answer to each question then forms the basis of the next question.

5 Whys Root Cause

Asking Why multiple times will help to drill down to the core of the problem and the root cause will become more apparent. This gives more depth to the problem-solving process and allows to look beyond symptoms and assumptions. Once the true root cause is identified, the chance for an effective solution will greatly increase.

This is often illustrated with the following simple example:

5 Whys Example
Notice the difference between the assumed cause and the root cause

Normally, asking Why five times in a row is enough to get you quite close to the root cause. Five seems to be is a good starting point, however, you may find that you need to ask Why more or less times depending on the situation. The goal is to get to a place where you can approach the core of the problem. The key with finding the root cause is to keep looking, you will eventually get to the true cause which you can act on right away.

Once you have discovered why a problem occurs, you then need to take corrective actions to solve the problem. Remember that each Why answer is a hypothesis that can be validated by testing the process. Validating the truth of every answer will help finding the true root cause, or at least, make sure you are supporting your answers with evidences and data.

5 Whys Lean Six Sigma
5 Whys is widely used within Lean and Six Sigma frameworks

5 Whys can be used individually or as part of a cause-and-effect analysis. It can be more effective when it is used in combination with other methods and techniques such as fishbone analysis, brainstorming and root cause analysis. Sometimes, you may have more than one factor that contributes to the problem. Other times, the problem is too complex to be analyzed in a straightforward manner.

When there is more than one factor contributing to a single problem, a fishbone diagram can be used to helps identify and arrange all possible causes. Once all possible causes are identified on the fishbone diagram, you can use the 5 Whys approach to drill down to the root causes for each possible cause. However, 5 Whys is usually best suited for simple problems with few or even one possible root cause. Complex problems often need more advanced analysis techniques.

5 Whys Usage Matrix
5 Whys is most effective when used to solve simple to moderate problems

5 Whys can also be used in troubleshooting and in process design to prevent problems from happening in the first place. It can be done in a team setting or on an individual basis. When it is undertaken as a team exercise, participants need to be aware of the problem. It will be more effective when the participants consist of front-end operators and Subject Matter Experts. Always involve people who are experienced in the process and seek help when needed.

How to Use the 5 Whys?

  • With your team, write a clear and specific problem statement. Ensure your problem is relevant and solving it will make a difference.
  • Ask “Why the problem occurs?”. Write the answer down below the problem.
  • Ask Why again for the generated answer and write the answer down.
  • Keep asking Why until the team identify the root cause of the problem, or until you get the answer “I don’t know”.
  • Once you are finished, discuss and agree on the corrective actions that will permanently correct the problem.

Note: Avoid vague or broad answers even though they may be true. Answers must be specific enough to help solve the problem.

Example – Delayed Test Results

In this example, a team used the 5 Whys approach to determine the reason behind a customer complaint about the delayed test results at a laboratory.

5 Whys Example

Notice in this example that only four Whys were required to get to what looks to be the root cause.

Example – Maintenance Department

This is another example that uses the 5 Whys approach to answer a concern during a Lean Six Sigma workshop.

5 Whys Example

Note that you can carry on asking Why and ask, “why doesn’t maintenance department have a schedule for routine activities?”. This will get you to a deeper level where you need to improve the business process in order to solve the problem.

Source: Smallpeice Enterprises (

There are many tools that can help you to use 5 Whys to analyze your problems. One of the simplest ways is to use this 5 Whys Template.

5 Whys Template Example
5 Whys template example

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