In plain English a root cause is a cause that is at a root of an effect. An effect can have more than one root. Thus a given effect can have, and usually does have, more than one root cause. In Continuous Process Improvement (CPI), a root cause is the most basic reason for a defect or problem in a product or process. Elimination of the root cause leads to the elimination of the defect or problem.

In order to be a root cause an item needs only two attributes: 1) it is a cause and 2) it is at a root. Root causes do not have to be correctable. They do not have to be under any one's control. They happen to have the attribute that if they are favorably modified the effect will also be favorably modified.

Tools such as the 5 Whys or the Fishbone or Ishikawa diagram are used to identify the root cause of a problem or defect as part of a CPI project aimed at improving product or process quality.

In using the Five Whys, the analyst should bear in mind that understanding the causation of an effect involves understanding the necessary and sufficient influences that resulted in the nature and magnitude of the effect.

In using the Ishikawa Fishbone Diagram the analyst should bear in mind that there are many versions of the Fishbone Diagram and that most are more properly classified as brainstorming tools rather than root cause analysis tools.

External link

• Meaning of Root Cause, Part I
• Meaning of Root Cause, Part II
• Root Cause at Six Sigma