5 Why Analysis

The 5 Why Analysis is a methodology used to investigate cause/effect relationships for a particular problem and identify a root cause. It is often used in the context of lean, six sigma, process improvement projects. Repeatedly asking the question “Why” allows you to peel away the layers of symptoms which can lead to the root cause of a problem. Note that the number 5 is a good rule of thumb, but some problems may take more or less levels to really get to the root cause. Also, sometime the underlying reason for a problem will lead to another question to be investigated.

The methodology is often applied with a fishbone or Ishikawa diagram, which allows you to lay out all the potential inputs and factors affecting a problem. The 5 Whys are a good way to then drill down into the details. The methodology is best used in a team setting, and it helps to discuss the various issues in depth and make sure the team comes away with an agreement before proceeding. Be careful not to “lead” the questioning in order to get to a preconceived answer.

Keep in mind also to think through reasons why a problem was not detected, and why the system allowed the problem to occur. All of these factors are helpful in developing a corrective action plan.