A common error of many six sigma and operations research professionals is not properly selecting the correct subgroup sampling technique when constructing a Statistical Process Control (SPC) chart. Incorrect subgroup sampling technique selection has become worse in the modern computing age – perhaps because most practitioners try to “fit” their data into the GUI template of the major statistical software packages. Consequently, many practitioners produce aesthetically appealing charts that are simply not effective at identifying out-of-control (OOC) conditions. This paper will discuss proper SPC subgroup sampling techniques and illustrate the principles of proper subgroup sampling selection from a practitioner’s perspective.

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