sigma represents standard deviation. In a normal distribution, +/- 1 sigma from the mean, for instance, corresponds to approximately 67% of the area under the normal distribution. +/- 2 sigma corrresponds to 95% of the area and +/- 3 sigma from the mean corresponds to 99% of the area under a normal distribution. The area that is covered under +/- six sigma from the mean corresponds to nearly 100% -- that is, the part of the area NOT under that +/- 6 sigma is in the 10^-15 range or 1/1,000,000,000,000,000.
The six sigma name borrows from this to suggest that the method gives this degree of certainty: that in 999,999,999,999,999 in 1,000,000,000,000,000 cases the result will be predictable. It does nothing, however, to explain how an agricultural process management methodology applies to other fields.
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If Six Sigma = 0.999999, then in percentage terms that would be 99.9999%.
3 Sigma is 66800 defects per million pieces 6 Sigma is 3-4 defects per million pieces You can check out the number of defective pieces per million & the % accuracy for all Sigma levels in the six sigma conversion chart in the related links section
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The capital sigma. The capital sigma. The capital sigma. The capital sigma.
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