Question

Please explain your answer. I will be giving a thumbs down to all the incorrect answers. Thanks for all your help.

The statement GE definition of 6σ is really equivalent to one of these answers · 4.5σ 沅, design 4ơ design design

Answer 1

Answer : 4.5 sigma

A Six Sigma process has a specification limit which is 6 times its sigma (standard deviation) away from its mean. Therefore, a process data point can be 6 standard deviations from the mean and still be acceptable.

In a stable process, the mean naturally shifts as much as 1.5 sigma in the long term on either side of its short-term value. The green lines in Figure 2 (below) show the extreme case of 1.5-sigma mean shift to the right. The right specification limit is at 4.5 sigma from the mean with a defect rate of 3.4 parts per million (PPM). The left specification limit is at 7.5 sigma from the mean with a defect rate of 0 PPM. The overall defect rate, therefore, is 3.4 PPM. A similar argument applies to the extreme case of 1.5-sigma shift to the left. A Six Sigma process is actually 4.5 sigma in the long term, and the 3.4 PPM defect rate is the 1-sided probability of having a data value beyond 4.5 sigma measured from the short-term mean.

SL SL 7.5v 4.5 o PPM 3.4. PPM

Figure 2: Process Mean Shift of 1.5 Sigma and Defect Rate Corresponding to 4.5 Sigma

The 1.5-sigma shift makes defects approach 0 on the opposite side of the shift even at lower sigma levels. The one-sided defect rate is applicable to any capable process with 1-sided or 2-sided SLs, even at a 3-sigma level.