There is a simple but effective technique for determining the root cause without resorting to the more complex tools and techniques included in the Analyse section of the Six Sigma DMAIC methodology - covered in depth on our Root Cause Analysis course as well as our Lean Six Sigma Green Belt, Black Belt & Yellow Belt courses:

The 5 Whys

A question every parent and teacher will be very familiar with, asking why is a great way of winding people up. Every time you ask why, someone has to explain the last reason they gave - narrowing down or opening up the original statement until the asker is happy - which can go on for a long time with children.

What makes asking why a workable solution for determining the root cause of a problem?

• It is an easy tool that requires little statistical analysis
• You document each step of the analysis so you always know the path to the root cause
• The root cause is found more often that not
• Multiple root causes are often stumbled upon during the process

Why 5?

5 has been identified as the optimum number of ways needed to find the root cause of a problem. Most root causes are identified around the 5th question but some more complex problems lead to more questions being asked.

How to Use the 5 Whys

1. Identify the problem and write it down.

2. Ask why the problem is happening and write it down the answer.

3. If that hasn't determined the root cause of the problem then ask why the answer to your first question is happening.

4. Repeat step 3 until you have identified the root cause.

When is Asking Why Appropriate?

The 5 Whys tool is best used when there are human factors involved in the problem. Asking why is a very good tool for discovering human error and bad judgement calls.

Download our DMAIC Methodology Tools Map for a complete list of the Lean & Six Sigma tools that we cover on our courses.

The 5 Whys in Practice

Here I am going to use a simplified scenario to show the 5 Whys in practice.

Problem: A bakery is losing money.

Why is the bakery losing money?

Customer numbers have dropped.

Why have customer numbers dropped?

Customers are switching to a rival bakery across the road.

Why are customers switching?

The rival bakery is cheaper.

In three questions the root cause of the problem has been identified, helping the manager choose the best course of action - lowering prices or improving quality to justify higher prices.

If the bakery manager wanted, they could even go further and ask why the rival bakery was cheaper - this may result in finding a cheaper supplier or a production method with less wastage.

Six Sigma is about finding problems & their causes to improve business processes and the 5 Whys can be a very useful and easy way of finding the root cause of a problem.

This is a very simple demonstration of the 5 Whys in practice but it shows that with a few questions you can easily find the root cause of a problem. It also prevents you from making the wrong judgement call by ensuring you are always asking the right questions.