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Whenever there’s a problem, an immediate response typically involves asking the question, “Why?” Though this is standard in everyday life, it’s also an important facet of Six Sigma – which features the Define, Measure, Analyze, Improve, and Control steps. The 5 Whys fit into the Analyze phase of this method. But what exactly does it mean, and how does it help in root cause analysis?

The Purpose of 5 Whys in Root Cause Analysis

The idea is that by asking “Why?” about 5 times, you can get to the bottom of just about any problem and not just a cursory view of a problem.   That doesn’t mean that every problem will need 5 Whys, but it’s usually a good place to start.

How the 5 Whys Work

The first step in the 5 Whys process is to document the problem at hand – don’t keep it all in your head – write it down for better clarity and be as descriptive as possible. Make sure the whole team is on the same page in describing the problem.

Next, ask “Why” this problem happened.   After you have defined your Level 1 “Why” it happened,  then repeat the process, asking “Why” the Level 1 problem occurred, then after answering that Level 1 question, ask why THAT happened, and so on.

If you didn’t find the root cause the first time, ask Why again and write down the answer that follows. Continue asking Why and providing answers until you have found the root cause. You can continue this method as many (or as few) times as necessary to solve the problem.

Toyota Corporation was a pioneer in continuous improvement and they developed what was known as the “Toyota Production System.”  One of the components was the 5 Why process and here is an example from their website:

Why #1     “Why did the robot stop”?

The circuit overloaded, causing a fuse to blow.

Why #2      “Why is the circuit overloaded”?

There was insufficient lubrication on the bearings, so they locked up.

Why #3       “Why was there insufficient lubrication on the bearings?”

The oil pump on the robot is not circulating sufficient oil.

Why #4      “Why is the pump not circulating sufficient oil?”

The pump intake is clogged with metal shavings.

Why 5       “Why is the intake clogged with metal shavings”?

Because there is no filter on the pump.

The 5 Why Process may also include the following “Whys” to help further dive into root cause and then move toward corrective action.

Why wasn’t the problem caught earlier in the process?

What wasn’t the problem prevented

Choosing the Right Team

Another important factor in a successful 5 Why process is getting the right team on board. This may not necessarily be  a team you normally work with, or that normally works together at all. The goal is to bring a diverse set of perspectives to come up with a range of answers for each question. Getting input from a broad group can offer new ideas that you yourself may not have thought of on your own.

By incorporating the 5 Whys strategy in problem solving, companies can more accurately and efficiently find the root cause of a problem. We’ve been implementing this process in our own operations and have found it to be an effective option in root cause analysis.

Author Name:
Randy P. Jones, Senior Engineering Technical Manager, CAB World
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