Sigma is also known as process capability. It is the capability of the process to produce defect free work. Higher the capability, lower the defects. As you can see in the table when a business process performs at Six Sigma capability, it only produces 3.4 defects in 1 million opportunities. Wow, that's a breathtaking number. As the Sigma level reduces to five sigma capability, it produces 233 defects in 1 million opportunities.

Furthermore, as the performance of the process dips to two sigma capability, the process is producing 308,537 defects in 1 million opportunities. Whoa. Restaurant bills, airline baggage, a doctor's prescription and service industries, which are people driven generally will fall at two sigma level. Average companies perform at three sigma best in class companies. Automobile organizations, among others operate at Six Sigma level of performance.