The term 6-sigma refers to a quality assurance process. It also means six standard deviations from the mean. A system that achieves the six standard level will have 3.4 or fewer defects per million opportunities.


Six Sigma is a quality program that, when all is said and done, improves your customer’s experience, lowers your costs, and builds better leaders.
-- Jack Welch

Certifications in 6-sigma are green belt, yellow belt, black belt, and master black belt.

Variations in the name use the words or the symbols for six / 6 and sigma / σ (The Greek letter named sigma, which is also the symbol for a standard deviation.)

A common 6σ methodology is referred to as DMAIC, which stands for define, measure, analyze, improve, and control. Variations include DMADV (Define, Measure, Analyze, Design, Verify) or DFSS (Design For Six Sigma). Multiple statistical techniques are used. Investigative techniques include the "5 whys" (keep asking why until you get to the root cause (root cause analysis).

It was originally designed to improve the quality of manufacturing processes. It is still used in manufacturing, and it is also popular in software development. Projects are often initiated to make changes that will achieve a higher level of quality.

Related: statistical sampling, regression analysis, SIPOC, control chart

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