5 Whys is a question-asking method used to explore the cause/effect relationships underlying a particular problem. Ultimately, the goal of applying the 5 Whys method is to determine a root cause of a defect or problem. It was developed at Toyota as part of their production process. In fact, the Toyota production system was built on this practice and the evolution of this scientific approach. As Taiichi Ohno, father of the Toyota production system stated:“Why does one person at Toyota Motor Company operates only one machine, while at Toyoda textile plant one young woman oversees 40 to 50 automatic looms?”
We obtained the answer by starting with this question: “The machines at Toyota are not set up to stop when machining is completed.” From this, automation with a human touch developed.
To the question, “Why can’t we make this part using just-in-time?” came the answer “The earlier process makes them so quickly we don’t know how many are made per minute.” From this, the idea of production leveling developed.
The first answer to the question, “Why are we making too many parts?” was “Because there is no way to hold down or prevent overproduction.” This led to the idea of visual control which led to the idea of kanban.
Often a 5 Why analysis is done at three different levels: the specific nonconformance; why the problem was not detected; and what systemically occurred that created the problem.
Asking why seems easy, but sometimes it is difficult to do. Some of the Whys can be answered using current process knowledge, but a more in-depth analysis will usually be needed to get to the true root cause. This can often include the use of other basic quality tools.
Here is an example of using the 5 Whys in an administrative area:
Observation: Our revenues were down 12% this quarter.
Why?: Because we sold fewer products, and the price stayed the same.
Why?: Our advertising presence was down 25%.
Why?: The ad budget request wasn’t received in time.
Why?: There was no advertising manager.
Why?: The position wasn’t posted as open for two months after the initial opening.
Why?: The manager of the advertising area was delinquent in sending the opening to personnel.
Note that Why was actually asked 6 times in this example to get to the root cause.
Once you’ve determined the root cause using the 5 Why process, you can use the, therefore, technique to make sure it makes sense. Using the admin example above, it would flow like this:
The manager of the advertising area was delinquent in sending the opening to personnel.
Therefore: The position wasn’t posted as open for two months after the initial opening.
Therefore: There was no advertising manager.
Therefore: The ad budget request wasn’t received in time.
Therefore: Our advertising presence was down 25%.
Therefore: We sold fewer products, and the price stayed the same.
Therefore: Our revenues were down 12% this quarter.
Repeating why five times can help uncover the root cause and correct it.
Keys to using the 5 Why process effectively are to make sure you start with a good problem description, confirm each cause before going to the next Why, reverse the process using the, therefore, technique, and verify all cause-effect relationships.