Six Sigma project methodology (DMAIC).

Six Sigma () is a set of techniques and tools for process improvement. A 6 sigma process is one in which 99.99966% of all opportunities to produce some feature of a part are statistically expected to be free of defects.

The main goal of this methodology is to improve manufacturing quality by identifying and removing the causes of defects and minimizing variability in manufacturing and business processes. It does this by using empirical and statistical quality management methods and by hiring people who serve as Six Sigma experts. Each Six Sigma project follows a defined methodology and has specific value targets, such as reducing waste or increasing customer satisfaction.

The term Six Sigma originates from statistical modeling of manufacturing processes. The maturity of a manufacturing process can be described by a sigma rating indicating its yield or the percentage of defect-free products it creates—specifically, to within how many standard deviations of a normal distribution the fraction of defect-free outcomes corresponds.

Brief History

This methodology was introduced by American engineer Bill Smith, while working at Motorola in 1986, as a quality management set of tools, strategies, and tactics to enhance customer satisfaction, employee development, and continuously improve processes to increase corporate profits, shareholder value, and achieve corporate excellence.

The term Six Sigma comes from statistics, specifically from the field of statistical quality control, which evaluates process capability. Originally, it referred to the ability of manufacturing processes to produce a very high proportion of output within specification. Processes that operate with this level of quality over the short term are assumed to produce long-term defect levels below 3.4 defects per million opportunities (DPMO).


6 Sigma asserts that:

  • Continuous efforts to achieve stable and predictable process results (e.g., by reducing process variation) are of vital importance to business success.
  • Manufacturing and business processes have characteristics that can be defined, measured, analyzed, improved, and controlled.
  • Achieving sustained quality improvement requires commitment from the entire organization, particularly from top-level management.

Features that set 6 Sigma apart from previous quality-improvement initiatives include:

  • Focus on achieving measurable and quantifiable financial returns.
  • Emphasis on management’s leadership and support.
  • Commitment to making decisions on the basis of verifiable data and statistical methods rather than assumptions and guesswork.


Wikipedia. Six Sigma.