What Metric? What Test?
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 This topic has 4 replies, 4 voices, and was last updated 8 years, 12 months ago by Robert Butler.

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June 18, 2012 at 4:43 pm #54101
KennettParticipant@AndrewKennett Include @AndrewKennett in your post and this person will
be notified via email.What metric? What test? One of our suppliers is wanting to change from approval based on a test results per batch (~100T batches) to blending batches and getting approval on calculated values. They will test each batch and then blend to meet our specs but in the long run wont have time to test the blend. We suspect that the blending does not give a simple average or weighted average and there is a fair bit of measurement error (besides the huge sampling error). To test that their blending calculation gives a reasonable estimate of the test parameters we will, initially, get both their calculated value, their test results and well do our own tests. So for each of 3 parameters we will have 3 data sets: calculated, supplier, inhouse. How best to test the accuracy calculated value?
0June 19, 2012 at 7:24 am #193594
MBBinWIParticipant@MBBinWI Include @MBBinWI in your post and this person will
be notified via email.Do you have experimental data on the blending process and how they control this process so that they know how much of batch A (at value X) to blend with batch B (at value Y) to get the acceptable value Q? If so, then you need to verify the measurement system for the blending operation to ensure that when they say they have added P tons you know that that is +/ some amount, and that that variation keeps the blend value at an acceptable level.
0June 20, 2012 at 4:10 pm #193606
Mike CarnellParticipant@MikeCarnell Include @MikeCarnell in your post and this person will
be notified via email.@AndrewKennett MBBinWI gave a great answer since I would venture to guess they are trying to reduce the amount of testing they do.
This may be another approach. Have them control the process inputs and the process so that they don’t have to test to figure out if they did it right the first time. There was some methodology that was supposed to work on that idea. Just can’t quite think of the name of it right now. Six something………………?
Just my opinion.
0June 20, 2012 at 10:55 pm #193609
KennettParticipant@AndrewKennett Include @AndrewKennett in your post and this person will
be notified via email.Thank you for your answers. we are running control charts so that should help visualise what is happening. And if there was only the calculated and 1 measured value for each parameter I could run a paired ttest but I have 2 labs testing. I suppsoe I could run a paired ttest calc v lab for each lab or I could run calc v average of the 2 labs but is there a test like the paired ttest for calc v lab 1 v lab 2?
0June 21, 2012 at 5:24 am #193610
Robert ButlerParticipant@rbutler Include @rbutler in your post and this person will
be notified via email.It sounds like “calc” is the gold standard and it sounds like there are two issues:
1. Relationship between calc and each of the labs.
2. Relationship between the labs.One possibility would be to run a paired ttest between calc and each of the labs. That would tell you if there is a difference between the gold standard and what the each of the labs are doing relative to the standard. Then, assuming you ran the test using split samples, you could run a paired ttest between the labs to see if they differ. Whether they differ or not you would probably want to also run a BlandAltman test of agreement between the labs as an additional check on agreement and bias. Since you would be running multiple tests on the same sample populations you would need to adjust the pvalue to account for this.
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