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Re: Cpk's relationship to AQL

From: Stan Hilliard
Date: 04 Nov 1999
Time: 23:45:43

Comments

Greetings Bill,

If you use the two-point method of calculating the accept/reject rule, you need both an AQL and an RQL. See the tutorial at www.samplingplans.com/modern3.htm

You can convert the AQL and RQL fractions defective into their corresponding Cpk indexes using the regular formula for Cpk: Cpk=Zaql*sigma/3. This is assuming that the sampling plan is for variables with known standard deviation.

You could also convert the horizontal axis of the oc curve produced by TP414 into Cpk units -- by hand. See www.samplingplans.com/programtp414.htm

The interpretation of the oc-curve would be "if the true lot Cpk were X, then the probability that the sampling plan will accept the lot would be Y. See www.samplingplans.com/modern3.htm#EVALUATE

Sincerely, Stan Hilliard


Last changed: November 20, 2007