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Sigma is a letter in the Greek alphabet used to denote the standard deviation of a process (standard deviation measures the variation or amount of spread about the process mean).
A process with "Six Sigma" capability means having 12 standard deviations of process output between the upper and lower specification limits. Essentially, process variation is reduced so that no more than 3.4 parts per million fall outside of the specification limits. The higher the Sigma number, the better. All processes vary, too much variation is costly.
The "Six Sigma" term also refers to a goal, and methodology utilized to drive out waste and improve the quality, cost, and time performance of any business. On average, one Six Sigma project will save an organization between $250,000 and $3 million. Black Belts with 100% of their time allocated to projects can execute five or six projects during a 12-month period, potentially adding over $1M of ROI per belt per year.
Six Sigma implementation is achieved through the deployment of a project-by-project system. We define a project as a structured and systematic approach to achieving Six Sigma levels of improvement in a given process. Each Six Sigma project can be of a different size and duration.
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