January 27, 2009

Six Sigma is a methodology for improving the quality of production. It was developed by the company Motorola in the early eighties, and it is successfully applied in many software development companies.

The purpose of Six Sigma is to make a product of constant quality with statistically measured estimation of defects, improvement of process for eliminating defects, and monitoring these improvements. Six Sigma is successfully applied for improving the organizations in various spheres.

While it has a successful reputation in big companies with thousands of employees, Six Sigma also may be applied in small design teams. This makes it being used by many small web development teams to improve their processes.

The basis of the methodology Six Sigma is made by an estimation of deviations of actual metrics of process from a curve of normal allocation of deviations. If those or other metrics of process are in certain limits of deviations, the quality of process results also remains high. In statistics it is accepted to name a unit of measure of deviations as “sigma”.

The appreciable effect is observed at deviation no more than 4,5 sigma; In this case the metric of number of defects on one million units of production makes 3,4. But this condition is fulfilled in stable processes. Productions usually aren’t stable. The inventors of methodology have come to a conclusion that the deviations of the process, called by its natural instability, give quality deviations at level 1,5 sigma.

service lean sigma DMAIC

Thus, if the target degree of quality is made by 4,5 sigma taking into account 1,5 sigma on deviations it is necessary to provide a degree of quality in 6 sigma. ”To reach such degree of quality in production, 99.9997 % from a total number of products should be of comprehensible quality (or 3.4 defects on one million possible).

Deviation is the important part of Six Sigma. Here what one of the pioneers and innovators of the methodology has said: “Our clients feel Deviation, instead of the Average.” All processes have some heritable deviation. There are no software processes which generate defects with a constant coefficient. Here Six Sigma is especially effective.

The purpose of Six Sigma is to think of each aspect of business as about a process which can be improved and can be measured statistically. The main tool is the approach consisting of 5 stages named DMAIC (define, measure, analyze, improve, control).


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