How is Six Sigma used?

Six sigma is a measurement scale upon which improvement / performance can be gauged or overall methodology that provides standardized problem-solving tools improvement. . In layman's terms, the idea is that by using basic statiscal tools to identify sources of variation that cause defects in your processes, you can attack each one of those sources of variation and decrease the number of defects your process generates. The concept of a Six Sigma process comes from a process which yields most of it's output within the specification limits required by customers. In the case of a six sigma quality process (1.5 sigma shifted), no more than 3.4 out of 1 million outputs that come out of a process are defective.

There are many commercial pages which will explain sixsigma, none of which can be linked here.