Like Lean, Six Sigma is a business strategy that improves the quality and efficiency of operational processes. However, Six Sigma differs in focus from Lean in that Six Sigma targets making processes more uniform and precise through an application of analysis supported by statistics. However, the targeted outcome of each is to streamline and improve processes, reducing waste and error. Six Sigma was originally developed by Bill Smith of Motorola in 1986 to eliminate manufacturing defects. Like in Lean, Six Sigma defines a defect or waste as any outcome, product, or service that 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 defects per million opportunities. This translates to processes capable of delivering defined high quality outputs 99.9997 % of the time.
