Six Experts’ Definitions – What is Six Sigma?

Since its first major implementation in the mid-1980s, Six Sigma has become synonymous with quality improvement.  Its roots, however, stretch back more than one hundred years to the early and mid-nineteenth century when Carl Friedrich Gauss showed how probability could be represented by a bell-shaped or “normal” curve that peaks around the mean or expected value and quickly falls off towards infinity. 

In the 1920s, the concept that would become Six Sigma took another step forward when Walter Shewhart showed that three sigma from the mean is the point where a process requires correction.   Another sixty years would go by before engineer Bill Smith presented the concept of Six Sigma to Motorola Chairman Bob Galvin who then incorporated the metrics into the company’s processes.  Six Sigma Black Belts arrived, things got ‘lean’ and we then arrive at to our first definition of Six Sigma provided by its developers and summed up nicely by Wikipedia:

Definition 1:  "Six Sigma is a set of techniques and tools for process improvement that seeks to improve the quality of the output of a process by identifying and removing the causes of defects and minimizing variability in manufacturing."

The Six Sigma standard strives for a process in which 99.99966% of all opportunities to produce some feature of a part are statistically expected to be free of defects (3.4 defective features per million opportunities).

Soon, though, Six Sigma began to grow and evolve.  Motorola expanded the definition to incorporate their new understanding.  James Stojan at Farragut.com explains.

Definition 2:   "Six Sigma can be seen as an “Improvement Methodology”.  It can be further subdivided into two process chains:  Define, Measure, Analyze, Improve, Control (DMAIC) – used for improving quality/service problems – and Define, Measure Analyze, Define, Verify (DMADV) – used for developing new products or processes."

Motorola then took Six Sigma even further by extending the ideals into a management system.  Renee O’Farrell at Demand Media defines it thusly:

Definition 3:  "As a management systems, Six Sigma drives clarity around the business strategy and the metrics that most reflect success with that strategy.  It provides the framework to prioritize resources for projects that will improve the metrics, and it leverages leaders who will manage the efforts for rapid, sustainable, and improved business results."

In recent years, experts have provided more general definitions that bring the three previous manifestations of Six Sigma together.  Henry Harvin of HenryHarvin.com defines Six Sigma as:

Definition 4:  "…a measure of quality that strives for near perfection.  Six Sigma is a data-driven approach and methodology for eliminating defects (driving toward six standard deviations between the mean and the nearest specification limit) in any process – from manufacturing to transactional and from product to service."

Jack Welch – former CEO of General Electric and one of the earliest proponents of Six Sigma – generalized even further when he stated that:

Definition 5:  "Six Sigma is a quality program that, when all is said and done, improves your customer’s experience, lowers your costs, and builds better leaders."

Six Sigma continues to evolve and be used in new and unique ways.  As such, its definition continues to evolve to reflect its use.  Geoff Tennant, in his book Six Sigma:  SPC and TQM in Manufacturing and Services, defines Six Sigma for the twenty-first century:

Definition 6:  "Six Sigma is many things, and it would perhaps be easier to list all the things that Six Sigma quality is not.  Six Sigma can be seen as:  a vision, a philosophy, a symbol, a metric, a goal, and a methodology."

Conclusion: So whether you define Six Sigma as a metric, a methodology, a management system, or something else entirely, it is a tool that can save you thousands, if not millions, of dollars when properly implemented.  Have a look for yourself and let us know what you think.

Additional Sources: 

http://www.storyofmathematics.com/19th_gauss.html  

http://www.isixsigma.com/new-to-six-sigma/history/history-six-sigma/