Basic Concepts of Six Sigma

Six Sigma Blue Stripes Horizontal

I recently came across a post titled Using Six Sigma to Improve Customer Experience and Service. As it touches on several topics close to my heart I read it with great anticipation and sadly even greater disappointment.

Since I feel the author misses the basic concepts of six sigma and the many improvement opportunities it offers support and services organizations I decided to attempt and correct some of the misconceptions and offer a different perspective to some of the points discussed.

First and most obviously missing is the fact that six-sigma is an iterative improvement process. DMAIC, therefore, is circular as shown in the chart attached to the original post rather than being a one time linear activity, at the end of which is the six-sigma nirvana stage of 3.4 defects per million.

Second, the statistical concepts behind six-sigma are never mentioned, nor is the meaning of 3.4 defects per million opportunities (known as DPMO). Here is a brief explanation. Sigma is a measure of spread of a normally distributed population, and measures the number of standard deviations fitting within a certain range. That range, in turn, is the acceptable performance range, so performance within that range is considered good, and outside of it is bad. To achieve one sigma, for example, about 68% of the population must be within the acceptable performance range, for two sigma, 95.5%, and so on, as shown below:

Sigma ValuePercentage Within Range
~68.2%
~95.5%
~99.73%
99.993666%
99.9999426697%
99.9999998027%

The last item I’d like to touch on is the need to make quality improvement, six sigma or otherwise, an inclusive initiative. It should ensure each and every employee understands the improvement process and expected results, and is able to make contributions.

Obviously, it is not possible to increase sigma levels by going through the phases of DMAIC without transforming service delivery, and it is extremely unlikely that a single journey through DMAIC will take you into six sigma performance levels. However, the benefits of improvement, even from one sigma to two sigma are enormous. So, the value in six sigma is in the journey and in creating the continuous improvement culture rather than reaching the elusive ultimate destination.

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