Like Lean, Six Sigma is a business strategy used to improve both the quality and efficiency of operational processes. Six Sigma differs in focus from Lean however, in that Six sigma targets making processes more uniform and precise through an application of analysis supported by statistics. The outcome of each, however is to streamline and improve processes, reducing waste and error. Six Sigma was originally developed by Bill Smith of Motorola in 1986 as a way to eliminate defects in manufacturing. Like in Lean, Six sigma defines a defect or waste as any outcome, product or service which fails to meet the customer's expectations. Thus, Lean and Six Sigma share a customer-centric philosophy.
The statistical term sigma ( ð ) refers to the standard deviation of a process, but also describes the variation present within any process. The standard deviation measures the "spread" or dispersion from the mean (average) from the BEST to WORST outcomes. To achieve Six Sigma level quality a process must have less than 3.4 million defects per million opportunities. This translates to processes which are capable of delivering defined high quality outputs 99.9997 % of the time!