Six Sigma is a disciplined, quantitative approach, based on defined metrics, for process and business improvement. It is being taught in the manufacturing, service, and financial industries and has been introduced at several universities. 

The Philosophy:

  • Know that Quality is a long-term effort.
  • Involve all levels of the organization.
  • Work with suppliers and customers, both internal and external.
  • Address the "human" side of systems.

The Methodology:

  • Process mapping.
  • Identification of important variables.
  • Statistical tools, especially Statistical Process Control and Design of Experiments.

How did Six Sigma get started?
Motorola developed Six Sigma to:

  • Reduce the number of defects.
  • Effect a Bottom Line Improvement.

Six Sigma applies to:

  • Operations,
  • Product Development, and
  • Business Systems.

Where did the term Six Sigma come from? 

Suppose a "bell shaped" process is centered between the upper and lower specification limits, and these limits are 6 standard deviations on either side of the average. This may be the best we can do on a short term basis. On a long term basis, however, the process may drift, and to account for this, an "allowance" is made of 1.5 standard deviations. A "Six Sigma" process is thus defined as a process in which the number of defects outside 6 minus 1.5 ( = 4.5) standard deviations from the mean is 3.4 defects per million opportunities in the long term. In other words, even with a shift of 1.5 standard deviations in the process, only 3.4 defects per million opportunities will be out of specification.

What are the benefits of Six Sigma, besides improving the bottom line?

  • Improved process understanding.
  • Elimination of assignable causes of variation.
  • Minimization of over control.
  • Improved product consistency.
  • Improved customer satisfaction.

Six Sigma effects:

  • A permanent change in the "people" infrastructure, which is robust to changes in the system, but which can adapt to change as needed.
  • Process improvements that continue beyond the initial effort.

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