Sampling


Question

Is there a sampling plan for determining the number of cases to pull in a batch from which you perform the ANSI/ASQ sampling of individual products?  For example: you receive 550 cases with 145 product vials/case.  Is it proper to sample a total of 500 vials from 25 cases (using square root of n+1) or would applying the ANSI/ASQ single level II be more appropriate?  We would then need to pull 500 vials from 80 cases.  Or is there a better statistical method?

Answer

There are two ways to answer this. One is to follow the standard and take samples from 80 cases until you get 500. It is assumed that the samples are random so that you do not always take the samples from the same location in the case.  That is following the standard.

The second is that you take a sample from 25 cases in a random manner.  That is fine also.  There are no standards for sampling from cases so either way will work.  Years ago, I developed a sampling scheme similar to what is proposed at the employer I was working with at the time.  Sometimes you have to be creative.

Jim Bossert

SVP Process Design Manger, Process Optimization
Bank of America
ASQ Fellow, CQE, CQA, CMQ/OE, CSSBB, CSSMBB
Fort Worth, TX

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