Root Cause Analysis (RCA): 5 Whys

One of the tools of continuous improvement, the 5 Whys technique can help, for example, with root cause analysis (RCA) when determining how to solve problems. With 5 Whys you look at the relationship of cause and effect. Your goal is to repeat the question “why?” enough times to get to an answer that will effectively solve the problem identified.

Putting 5 Whys into a context

When you look at the Six Sigma tool of DMAIC (define-measure-analyze-improve-control) you can use 5 Whys in this context during the Analyze phase. The 5 Whys approach can be effective if you do not need to collect data, for example, to get to a root cause. You use the 5 Whys when one answer leads into the next question and find a root cause that way.

Some benefits of the 5 Whys approach include that it:

• Is simple
• Is easy
• Can show the relationship of the cause and the problem
• Can show a root cause
You can use 5 Why on a daily basis with or without a Six Sigma project. It can also be helpful when human intervention can help to solve a problem.

A way to use the method

Here is an example of how you can use 5 Whys.

1. Document a problem
2. Use a team approach
3. Continue to ask why you have the problem until you find the root cause
4. Ask why as many times as needed to get consensus from the group on the reason for a problem

You can also use 5 Whys to fill in the bones of a fishbone diagram. You define the problem in the main part of the fish and put in the causes on the rest of the diagram. This is another tool you can use to determine root causes and subsequent solutions.

An example

Imagine your group makes a product that does not meet the the specifications of the customer. Customers are asking for red plastic cups. Instead they are getting blue ones.

Problem: Customers are unhappy because they are getting blue cups instead of the red cups they ordered

1. Why are customers getting blue cups instead of the red cups they ordered? – This is because manufacturing gets instructions to build something different from what the customer orders
2. Why is manufacturing getting instructions different from the order? – This is because an error happens when the order gets entered.
3. Why does the information get entered with a mistake? – This is because a form does not indicate what color to make and manufacturing defaults to blue.
4. Why does the form not indicate the color? – Because the form was not updated when the default process began.
A solution to this problem – with four whys asked – could be to update the form. The team could update and check to make sure this solves the problem.

Some guidelines

We just looked at how a 5 Whys approach can help uncover a cause and effect relationship and help to solve problems. You ask the first Why question, then determine the next, and so on until you have a solution you think will work. You might also uncover more than one root cause. When using the technique, we should know:
• you could need more than 5 Whys or less
• you might ask “Why did the process fail” as one of the 5 Whys
• you should put the focus on the process not the people
• this technique can work for Kaizen, Lean, and Six Sigma
• you can use a table or fishbone to collect answers

Here are some more guidelines

1. Use 5 Whys with the right group of people
2. Use paper or a white board
3. Write down the problem
4. Look at causes not just symptoms
5. Make answers precise
6. Use facts and knowledge
7. Assess the process not the people
8. Do not use human error as the cause
9. Remember the customer’s point of view

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