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GN19
Level II

Is there a way to get Westgard rules to apply to user defined control in Levey Jennings?

I have a script that runs two variations of a Levey Jennings, one using data set determined 2 sigma control limits which then correctly applies Westgard rules and the other with user defined defined limits that does not apply Westgard rules based on these inputs. Is there a setting to get Westgard rules to identify user defined limits as the 2 standard deviation calculation?


In the included image, I have 2 lots of controls in the example one with Levey Jennings limits sigma and one user defined. The user defined as described does not update the Westgard rules to these new limits. Any help is appreciated! 

4 REPLIES 4
GN19
Level II

Re: Is there a way to get Westgard rules to apply to user defined control in Levey Jennings?

Please let me know if I need to clarify anything! 

Re: Is there a way to get Westgard rules to apply to user defined control in Levey Jennings?

I tried to match your situation. I created a L-J chart with two phases. I set sigma, and I was able to use the Westgard rules. I set the control limits, and I was able to use the rules, too.

GN19
Level II

Re: Is there a way to get Westgard rules to apply to user defined control in Levey Jennings?

Here are a couple more images in case you can catch my error. The first is the L-J chart with fake limits I defined and have my sigma at 0.6775 but the westgard rules are flagging samples within that value as 1:2S as if they are being applied to the autogenerated analysis of the population. The second image is my _LimitsKey I am importing for the control chart script to read. Please let me know if any more information or visuals would be helpful to see. Thank you! 

Re: Is there a way to get Westgard rules to apply to user defined control in Levey Jennings?

Here is information from my colleague, @tonya_mauldin, an expert in Control Chart Builder:
"When the specified limits do not equal Avg +/-  3*sigma limits, the Westgard Rules are based on the zones.  If the user adds zones they should be able to tell that the Westgard rules are, in fact, using the user-defined limits.  In his image, the distance from the center line to the upper control limit is smaller than the distance from the center line to the lower control limit.  The zones are calculated using the smallest distance, so for this case, they will be calculated using the distance from the center line to the upper control limit."