Basic Process Equation

One of the fundamental Six Sigma concepts is that the outputs of any process can be controlled by controlling process inputs. By controlling and transforming key process input variables (KPIVs) an organization can reduce process variation and significantly improve probability for achieving desired outcomes also known as key process output variables (KPOVs). There may be thousands of process inputs influencing performance of a system but not all inputs and processes are equally important. In order to achieve breakthrough results it is necessary to identify critical-to-quality (CTQ) requirements, define key processes that must be performed well, eliminate or minimize errors, mitigate the impact of uncontrollable input variables, and focus on a few critical inputs that really matter. This elementary Six Sigma concept is expressed mathematically using a simple and elegant equation: Y = f(X), where Y indicates desired outputs or outcomes (dependent variables); X represents inputs required to produce the outcomes (independent variables); and f stands for process or function performed on the inputs to produce the outcomes. To embrace simplicity, the figure below presents the key process inputs and outputs from a macro-level perspective.