The 1.5 Sigma Shift: What It Is and Why It Matters

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The 1.5 Sigma Shift: What It Is and Why It Matters

One of the most persistent points of confusion in quality engineering is the difference between traditional statistical process capability analysis and the Six Sigma approach. Specifically, why does Six Sigma define a “six sigma” process as having 3.4 defective parts per million (DPPM), when a straightforward application of statistical tables suggests that six standard deviations from the mean should correspond to a far lower defect rate—about 2…