History of Six Sigma

Six Sigma is a measurement standard in product variation that can be traced back to the 1920’s when Walter Shewhart of Western Electric produced a “three sigma” approach; three sigmas away from the mean is the point where a process needs to be corrected.

The mathematical principles of Six Sigma come from Carl Friedrich Gauss who introduced the ‘normal curve’ or ‘bell curve’. This is a graph which plots the number of samples in the vertical axis against their measured values in the horizontal axis. Most samples hold a value that is close to the average, so the curve is highest at the middle value. The farther the measured value is from the average, the fewer samples are found, and the curve is lower at each end. With a normal distribution curve, 99.7% of the data is expected to lie within +/- 3 sigmas from the mean.The statistical term “sigma” is a measurement of the area under the curve and identifies the number of defective units within a specific sample size

The modern concept of Six Sigma was developed in 1986 by Motorola engineers Bill Smith and Mikel J Harry. Motorola introduced the technique, setting an objective of Six Sigma for all its manufacturing procedures. Motorola has registered and trademarked the term “Six Sigma”. Since its establishment at Motorola, Six Sigma has been acquired and used to improve process quality and performance in a vast number of other businesses. The most notable instance is that of General Electric. CEO Jack Welch made Six Sigma central to the business strategy in 1995. The Six Sigma effort was hugely successful and sparked a distinct change of the employee's outlook towards quality, as well as contributing $700 million in corporate benefits in 1997.