How calculate the number of samples

L

lmoreno12

#1
I have some doubts about how do i know the best or the minimum number of values that i need to calculate Cmk, Cpk, or Ppk. Because i cant find in the Standard SPC (Manual from AIAG), that references all the rules of SPC. Exist a minimum number of values that i can use or i need to calculate the number of samplers for each study that i will make, considering the batch ?

Sorry for my english.
 
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Steve Prevette

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#2
Dr. Shewhart's original criteria was do not declare a process to be stable without a minimun of 25 sets of 4 data values.
 

Miner

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#3
The confidence intervals around a capability metric such as Cp/Cpk are extremely wide until you reach a sample size of 100. At that point you reach the point of diminishing marginal returns.

The reason for this is that you have uncertainty around both the mean and the standard deviation, and you use both terms when calculating a capability metric.
 
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