Motorola developed a concept called Six Sigma. Six Sigma focuses on defect rates, as opposed to percent performed correctly.

“Sigma” is a statistical term meaning one standard deviation. Six Sigma means six standard deviations. At the Six Sigma statistical level, only 3.4 items per million are outside of the acceptable level. Thus, the Six Sigma quality level means that out of every one million items/opportunities 999,996.6 will be correct, and not more than 3.4 will be defective.

 Sigma level           Defects per million opportunities

Level 1                  690,000

 Level 2                  308,537

 Level 3                  66,807

Level 4                  6,210

Level 5                  233

Level 6                  3.4 






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