Most people spend twelve or more years in an educational system in which grades of 90%, or higher, are considered excellent. However, in industry, 90% is not a good quality record. For example, if one out of every ten tires fails, you have a 90% quality rating, but that is totally unacceptable to tire customers.
Motorola developed a concept called “Six Sigma Quality” that 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 counted, 999,996.6 will be correct, and no more than 3.4 will be defective.
Experience has shown that in most systems, a Four Sigma quality level is the norm. At the Four Sigma level there are 6,120 defects per million parts, or about 6 defects per 1,000 opportunities, to do a task correctly.
· The key focus of companies implementing a Six Sigma program is to develop a good business strategy that balances the cost, quality, features and availability considerations for products. A valuable lesson learned is that decisions made must be tied to the bottom line for the company.