What is Sigma Performance?
Sigma Performance measures process performance relative to customer requirements. It takes into account some degree of undetected, non-random variation (“shift”). Unlike the Capability Index, all qualities, both measurable and countable, can be combined into a single scorecard. Sigma can be normed to the complexity of the process, using defects per million opportunities (DPMO) to facilitate comparisons across different processes. I thought “sigma” referred to the standard deviation of data. It does, and for measurable data, Sigma Performance is directly related to the standard deviation. The two uses of the term “sigma” should not, however, be confused.
