Definition C - What the "C" in C=0 Sample Plan means

Q

QE-Bob in Wisc

#1
Someone asked me what the "C" in C=0 meant, I thought it stood for charachteristic but someone believes that is incorrect but does not have an answeer themselves. Does anyone want to chime in?

Thank in advance.
 
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Michael_M

Trusted Information Resource
#3
Re: C=0 Sample Plan

On one of our customers quality documents, they say "C=AQL sample size per (blah blah), c=0". In this case, they are saying that we are required to AQL sample unless the PO says "per c" or some such.

It is very confusing if you are not VERY careful about case sensitivity.
 

Steve Prevette

Deming Disciple
Leader
Super Moderator
#4
A c=0 sample plan is one in which you do a certain number of samples (n). If you have zero failures (c) in those n samples, the test passes. If you have one or more failures, the plan fails. Basically, you stop sampling on the first failure.

Some "famous" c=0 plans include a sample size of 29 (if there are zero failures, I am 90% sure that the failure rate is less than 10%) and 59 (if there are zero failures, I am 95% sure that the failure rate is less than 5%).

Other plans allow you to have a couple of failures out of the number of trials. This reduces false alarm rates but requires a bigger sample size for the same AQL. A c=2 n=100 plan says I sample 100 items, and pass on 0, 1 or 2 failures, reject on 3 or more failures.
 

rickpaul01

Involved in HankyPanky
#5
Someone asked me what the "C" in C=0 meant, I thought it stood for charachteristic but someone believes that is incorrect but does not have an answeer themselves. Does anyone want to chime in?

Thank in advance.
I believe it goes back to MIL-STD-105 where "c" is defined as "single sample acceptance number". (maybe older) and I suspect it comes from the OC curve. The term "c=0" I think was coined by Nicholas Squeglia. It is defined as a sampling plan which does not allow for the acceptance if any defects are found. It would be disingenuous to try and extract the c from c=0 since the term is "c=0". (To me, it's like asking what the k in kleenex is.)
 
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