Determination of the Optimal Sampling Number

V

vicenteC

#1
Hello all,

We are currently measuring 5 properties from a membrane roll, the pass/fail criteria the average of all points is between a tolerance. This tolerance set up by the client.
Currently we are measuring from 24 to 10 different points of the roll depending the property, from the west to the east of the wide.
Theoretically speaking, the properties across West to East should be the similar.
So potentially I can have a good chance to reduce the number of samples from 24 or 10 to 2.
For this I carried out a SPC analysis of the variance, determining the Between/ within sample variance. getting what is the variance associated to within the sample and the variance to sample to sample.
When I take the historical data, and I delete the measurements leaving just 2 the variance is barely the same. :agree1:

Making a ratio btween the full testing and 2 points tested is really close to 1.
So this may show me that I am in the right direction, unfortunately this is not a proof or evidence enough to reduce the number of tests.

Ho can I address a testing or hypothesis to prove that the reduction of testing is OK?

Thanks for the feedback
 
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Bev D

Heretical Statistician
Staff member
Super Moderator
#2
Re: Optimal Sampling number

Can you post your SPC data? (Leave in all data points)
 
V

vicenteC

#4
So after analyzing the data, my biggest concert is:
Is any difference between groups? from West11 to Eest11?

If we take a look to the attached picture we see a minimal deviation between west and East point (graph 1 to 24) across all the lot numbers. Getting a small deviation between the groups compared to the overall
So the question is can I reduce the number of samples to 2? C11 and C12
If I eliminate the data leaving 2 points the results extremely similar , so I may assume that measuring 2 points instead of 24 is not dangerous.



You opinion
 

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Bev D

Heretical Statistician
Staff member
Super Moderator
#5
can you explain what the test locations mean?

maybe provide a diagram?

I assume you are measuring something across and along a web?
 

Bev D

Heretical Statistician
Staff member
Super Moderator
#7
OK so W=west and E=east. I get that. C = center?
and what is different about E11 and E12 and E21...

sorry to appear dense but I deal with many industries and processes and nomencalture can be 'custom' and confusing to outsiders...in trying to understand and help with complex processes it is essential to understand the process in order to make sense of the data...
 
V

vicenteC

#8
Hello Bev,

Yes C1 and C2 are center the differences between C11 and C12 are that 11 belong to the beginning and C12 to the end.

From the chart we can observe that the beginning is always higher than the end , but that is not the case.

Theoretically I am measuring a flat surface across the width and the properties should be the same that is why my initial approach is to eliminate all measurements but C11 and C12.

Thanks for the follow up
 
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