Six Sigma Six Sigma is a business philosophy focusing on continuous improvement, based on a statistical measure of variability. In a service or manufacturing environment, a Six Sigma process would be virtually defect free. In a million operations of a process, Six Sigma allows only 3.4 defects. Most companies operate at four sigma which allows 6,000 defects per million operations of a process. in NCSUwith businessdefectsmillionpersigmasixstatistical