5 Why and 2 How (5W and 2H)

The 5 Why (5W) and 2 How (2H) method of problem solving is commonly used in Six Sigma projects.  It is a structured approach that investigates and defines a problem by asking a specific set of questions.  The questions are related to a previously defined opportunity or problem statement.

The 5W’s and 2H’s stand for:
Why 1: What?
Why 2: Why?
Why 3: Where?
Why 4: Who?
Why 5: When?
How 1: How did it happen?
How 2: How much did it cost?

These techniques are used to get to the root cause of a problem. It is the practice of asking five times or more why the failure has occurred in order to get to the root cause. Each time an answer is given, you ask why that particular condition occurred.  Not all problems have a single root cause. If one wishes to uncover multiple root causes, the method must be repeated asking a different sequence of questions each time.

The method provides no hard and fast rules about what lines of questions to explore, or how long to continue the search for additional root causes. Thus, even when the method is closely followed, the outcome still depends upon the knowledge and persistence of the people involved. –(Wikipedia)

These methods are taught at the Green Belt and Black belt levels of Six Sigma.
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