Q: Should we change our 2 SD manufacturer range to a 3 SD manufacturer range?

"What is the solution if the quality control comes with 2 SD, do we need to change the product to a 3 SD control?"

Another question from our Cut Your QC webinar, still available on demand at

https://us02web.zoom.us/webinar/register/WN_F5IRlqySRR6eRcrm9Zz9mQ

I believe this question is referring to the range that comes with the control. The manufacturer typically gives a range, meant to be a range of means (that is, you should find your mean inside this range), which some laboratories adopt as their actual control range.

When we talk about moving to 3 SD, this refers to the actual QC rules being used on the method. Instead of the typical 1:2s rule, a 6 sigma test can use a 1:3s rule. But this rule must be based on the actual mean and sd of the laboratory. It cannot be used on the manufacturer's range, because the SD given from the manufacturer does not represent the actual SD of the laboratory.

So a laboratory can use different (and better and fewer) QC rules when they apply Westgard Sigma Rules, but only if they use an honest foundation built with their own mean and own SD. You can't deploy Westgard Sigma Rules on someone else's mean or SD.