Once the tools of the improvement phase have been used the Six Sigma project team will focus on attaining the necessary Sigma Level. After all, the goal of the improvement is to determine what level of Six Sigma is being met, what could be achieved, what should be achieved, and what the goals for improvement and control should be.
The Sigma levels used in Six Sigma help a company to determine their level of defects and where they fall in terms of their level of improvement. The term "Six Sigma" comes from mathematical statistics. “Sigma” is a term used to denote variance from the mean average of an event. It is understood that for any event or activity, 3 measures of these variances on either side of the mean average will include almost all potential activities. Let’s put this in some perspective.
- At the 5th Sigma level 233 defective parts per million occur.
- At the 4th Sigma level 6,210 defective parts per million occur.
- At the 3rd Sigma level 66,807 defective parts per million occur.
- At the 2nd Sigma level 308,538 defective parts per million occur.
- At the 1st Sigma level 690,000 defective parts per million occur.
To put this into further perspective, are you comfortable with an airline that has a crash rate at the 3rd Sigma level? If you have a surgeon who is performing your surgery are you comfortable with a surgical outcome rate at the 2nd Sigma level? Probably not. Customers drive the market and feel more comfortable with business and companies functioning more at the 5th or 6th level of Sigma. Most often, the 6th Sigma level. This chart provides a visual display of the Six Sigma levels.