Six Sigma Methodology: What it is, what it is not?

Six Sigma Methodology can be described by many different terms and phrases: Statistical Method, a gauge for processes and products, a systematic way how to act, a philosophy, a global language, etc. It is a way to live!

Six Sigma can be considered as a customer-based methodology. In every phase, in every act there always is the customer and his requirements involved. Customer satisfaction is the most important factor, a gauge, when estimating the results and succeeding of quality improvement. "The customer is the King" is the solid basement on which the whole methodology is built.

It gives to its user tools, with which it is possible to reach almost as a number of statistical defects: zero. As mentioned earlier quality of 99 % (= 3,8 Sigma) is not sufficient enough, but a quality of 6 Sigma (= 99,99966 %) is the only reachable goal. In addition the vision and the strategy to get this very huge goal is offered. (Figure 1)

Figure 1 - Normal Distribution Illustrates Three Sigma and Six Sigma Parametric Conformance (Breyfogle III, F. W., 1999)

Six Sigma is not one single but many small and separate steps together. It is not, however, nothing new or wonderful, it certainly is neither a miracle nor a magic trick. It is based on existing process data and statistical tools. Sigma (s) is a term from mathematics, statistics, describing variance measured from process. As a gauge in a process s describes the efficiency and ability to act accurately. The greater is the s-based key figure the more efficient is the process and the less it produces products and/or services with poor quality.

Table 1 shows information of the effect s-level has on its capability. I.e. in yield, loss production and time being down annually. According to this table the dramatic increase of yield with the increase of sigma-level is very clearly seen. The trend alike can been seen also in all other gauges.

Table 1 The Effect of Six Sigma-level on Capability of a Process

Please notice that only a few companies are "best-in-class", i.e. on 5,5 - 6 s level. The average companies - even good ones - are on 3 - 4 s level.