<p>Quality Control is a term often used within production and is referring to managing processes so they produce capable products. Within Quality Control, process capability index is a common measure to oversee processes. Safety Region Plots were introduced to do this graphically. In Albing & Vännman (2010) the concept of Safety Region Plots is expanded to incorporate an elliptical shape. The method of Elliptical Safety Region Plots assumes a normally distributed data. In this paper we are looking at the robustness of the Elliptical Safety Region Plots if we can assume a symmetrically, but non-normal, distribution. In the results we can conclude that an adjustment is required for symmetric, but non-normal, data if the method in Albing & Vännman (2010) is going to be used. An eventual adjustment is discussed in discussions. To easily be able to use the Elliptical Safety Region Plots mentioned in Albing & Vännman (2010) we have developed a program in RExcel.</p>

Quality Control is a term often used within production and is referring to managing processes so they produce capable products. Within Quality Control, process capability index is a common measure to oversee processes. Safety Region Plots were introduced to do this graphically. In Albing &amp; Vännman (2010) the concept of Safety Region Plots is expanded to incorporate an elliptical shape. The method of Elliptical Safety Region Plots assumes a normally distributed data. In this paper we are looking at the robustness of the Elliptical Safety Region Plots if we can assume a symmetrically, but non-normal, distribution. In the results we can conclude that an adjustment is required for symmetric, but non-normal, data if the method in Albing &amp; Vännman (2010) is going to be used. An eventual adjustment is discussed in discussions. To easily be able to use the Elliptical Safety Region Plots mentioned in Albing &amp; Vännman (2010) we have developed a program in RExcel.