Management Systems Inc

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Determine The Root Cause: 5 Whys

Posted by isoeasy on May 19, 2006

The 5 Whys is a simple problem-solving technique that helps users to get to the root of the problem quickly. Made popular in the 1970s by the Toyota Production System, the 5 Whys strategy involves looking at any problem and asking: “Why?” and “What caused this problem?”

Very often, the answer to the first “why” will prompt another “why” and the answer to the second “why” will prompt another and so on; hence the name the 5 Whys strategy.

Asking "Why?" may be a favorite technique of your three year old child in driving you crazy, but it could teach you a valuable Six Sigma quality lesson. The 5 Whys is a technique used in the Analyze phase of the Six Sigma DMAIC methodology. It's a great Six Sigma tool that doesn't involve data segmentation, hypothesis testing, regression or other advanced statistical tools, and in many cases can be completed without a data collection plan.

By repeatedly asking the question "Why" (five is a good rule of thumb), you can peel away the layers of symptoms which can lead to the root cause of a problem. Very often the ostensible reason for a problem will lead you to another question. Although this technique is called "5 Whys," you may find that you will need to ask the question fewer or more times than five before you find the issue related to a problem.

Benefits Of The 5 Whys

> Help identify the root cause of a problem.
> Determine the relationship between different root causes of a problem.
? One of the simplest tools; easy to complete without statistical analysis.

When Is 5 Whys Most Useful?

> When problems involve human factors or interactions.
> In day-to-day business life; can be used within or without a Six Sigma project.

How To Complete The 5 Whys

1. Write down the specific problem. Writing the issue helps you formalize the problem and describe it completely. It also helps a team focus on the same problem.
2. Ask Why the problem happens and write the answer down below the problem.
3. If the answer you just provided doesn't identify the root cause of the problem that you wrote down in step 1, ask Why again and write that answer down.
4. Loop back to step 3 until the team is in agreement that the problem's root cause is identified. Again, this may take fewer or more times than five Whys.

5 Whys Examples

Problem Statement: The machine stopped working.

1. Why did the machine stop?  It blew a fuse.
2. Why did the fuse blow?   The fuse was the wrong size.
3. Why was the wrong size in the fuse box?  The engineer put it there.
4. Why did the engineer do that?  The supply room issued the wrong size fuse.
5. Why?  The stock bin was mislabeled

Problem Statement: Gage was found in use on shop floor beyond its calibration date.

1. Why was a gage in use beyond its calibration date? Because the gage was not recalled and the operator did not check the calibration label. 
2. Why was the gage not recalled? Because the gage was not on the recall list.
3. Why was the gage not on the recall list? Because the gage was just recently purchased.
4. Why are new gages not added to recall list? Because there is no procedure or specific training on purchasing gages.
5. Why did the operator not check the label? Because the operator was recently hired and had not been trained to check calibration labels.
6. Why wasn't the operator trained to check labels? Because on-the job training does not specify and it was overlooked.
7. Why doesn't OJT address calibration labels? Not considered a priority by supervisors.

The final Why leads the team to a statement (root cause) that the team can take action upon.

5 Whys And The Fishbone Diagram
The 5 Whys can be used individually or as a part of the fishbone (also known as the cause and effect or Ishikawa) diagram. The fishbone diagram helps you explore all potential or real causes that result in a single defect or failure. Once all inputs are established on the fishbone, you can use the 5 Whys technique to drill down to the root causes.

Key Points:
The 5 Whys strategy is an easy and often-effective tool for uncovering the root of a problem. Because it is so elementary in nature, it can be adapted quickly and applied to most any problem. Bear in mind, however, that if it doesn’t prompt an intuitive answer, other problem-solving techniques may need to be applied.


14 Responses to “Determine The Root Cause: 5 Whys”

  1. Mark Paradies said

    I’ve rarely seen 5 Whys result in finding true root causes. People usually stop at symptoms and think they have found root causes.

    For two articles about this see:



  2. […] Because the operator was recently hired and had not been trained to check calibration labels. 6. Why wasn’t the operator trained to check labels? Because on-the job training does not specify and it was overlooked. … Read More … […]

  3. […] Determine The Root Cause: 5 WhysBecause the operator was recently hired and had not been trained to check calibration labels. 6. Why wasn’t the operator trained to check labels? Because on-the job training does not specify and it was overlooked. … […]

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