TABLE OF CONTENTS You shouldn't attempt to do statistically driven improvements until you have a steady process.
W. Edwards Deming
Jack Welch was enormously successful at General Electric. His success is, at least in part, attributed to the use of Six Sigma in improving their operational and resulting financial performance. If we use Six Sigma, the logic goes, then our company is more likely to be successful. While this logic is admittedly too simplistic, it does seem to ring a cord in many circles, perhaps more so in companies looking for the next big step change in improvement. However, it may be that step change or overnight success takes about 10 years, no matter what course you take. Below is a review of Six Sigma according to Pande et al.,1 along with additional commentary.
Taken literally, Six Sigma is a statistical term which characterizes your quality having <3.4 defects per million for a given product or process specification. Table 10-1 provides the defect rate for one through six sigma levels of performance.
| Meets Specification Rate | Defect Rate | Sigma |
|---|---|---|
| 30.9% | 691,000 ppm | 1 |
| 69.2% | 308,000 ppm | 2 |
| 93.3% | 66,000 ppm | 3 |
| 99.4% | 6,210 ppm | 4 |
| 99.98% | 320 ppm | 5 |
| 99.9997% | 3 ppm | 6 |
However, Six Sigma has become a methodology for reducing the variability of processes such that the result is greater quality and consistency and better performance. According to Pande et al., it stresses the simultaneous achievement of seeming...
