What is Six Sigma ?

Six Sigma is an important measure of the quality of a system, being adopted by many top-class corporations the world over such as GE. Six Sigma has spawned an industry of its own, in terms of experts who go to corporations and figure out how these companies can improve their processes so as to meet Six Sigma quality standards, and there are teachers who give instructions as to how to become a Six Sigma expert. Six Sigma was initially implemented by Motorola, and is now adopted the world over. Six Sigma is primarily used in manufacturing and business practices, and seeks to improve the quality of process outputs by identifying and removing the causes of defects (errors) and variations. Six Sigmas has its own infrastructure, such as - It uses a set of quality management methods, including statistical methods, and creates a special infrastructure of people within the organization ("Black Belts" etc.) who are experts in these methods. Six Sigma was originally developed as a set of practices designed to improve manufacturing processes and eliminate defects, but its application was subsequently extended to other types of business processes as well. In Six Sigma, a defect is defined as anything that could lead to customer dissatisfaction.
Sigma (the lower-case Greek letter σ) is used to represent the standard deviation (a measure of variation) of a statistical population. The term "six sigma process" comes from the notion that if one has six standard deviations between the process mean and the nearest specification limit, there will be practically no items that fail to meet specifications.

As a comparison of the various quality norms:
Short-term sigma levels correspond to the following long-term DPMO (defective parts per million opportunities) values:

* 1 sigma = 690,000 DPMO = 31% efficiency
* 2 sigma = 308,000 DPMO = 69.2% efficiency
* 3 sigma = 66,800 DPMO = 93.32% efficiency
* 4 sigma = 6,210 DPMO = 99.379% efficiency
* 5 sigma = 230 DPMO = 99.977% efficiency
* 6 sigma = 3.4 DPMO = 99.9997% efficiency

Put another way, this reads as “3.4 defects per million opportunities to make defects”. This is a very high level of quality, and it takes a lot of effort, hard work, and process improvements to reach this level. Six Sigma is also being implemented by many software development companies for their projects.