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Refers to cause and effect and is a tool for root cause analysis. An output variable Y is dependent on the Inputs of one or more Independent Variables, X. Lean Six Sigma projects focus on improving Y, through the improvement of a ‘key’ X variable. That Means we should be treating causes, not symptoms. Y=f(X) analysis is also used as a brainstorming tool for identifying project opportunities and as a tool to ensure that the project is properly focused.


Customer response times (Y) at a call center are a function of the staffing levels (X). Thus, to reduce the response time, the staffing levels would need to be improved.