When and How to Use Zero Acceptance Number Sampling

Zero acceptance sampling plans are viable when suppliers are confident in their quality level

William A. Levinson

April 11, 2019

Inspection is a mandatory but nonvalue-adding activity, and our objective is to do as little as possible, provided that we continue to fulfill the customer’s requirements. The zero acceptance number (c = 0) sampling plan requires far less inspection than the corresponding ANSI/ASQ Z1.4 (formerly MIL-STD 105) plan, and becomes viable when the supplier is extremely confident in its level of quality.1

An ANSI/ASQ Z1.4 plan consists of a sample size n, and an acceptance number c. The inspector checks n items, and accepts the lot if c or fewer defects or nonconformances are found. These plans are designed to give (roughly) a 95-percent chance of acceptance at the acceptable quality level (AQL), which is one of the parameters for the plan’s selection.

The c = 0 plan, on the other hand, rejects the lot if any defects or nonconformances are found, but it requires a considerably smaller sample size. The drawback is that the producer’s risk (α) of rejecting a lot at the AQL is usually far greater than the textbook 5 percent, so the c = 0 plan should be used only when quality is much better than the AQL. This reinforces a basic principle of industrial statistics: We can have low risks or small sample sizes, but we can’t have...

About The Author

William A. Levinson’s picture

William A. Levinson

William A. Levinson, P.E., FASQ, CQE, CMQOE, is the principal of Levinson Productivity Systems P.C. and the author of the book The Expanded and Annotated My Life and Work: Henry Ford’s Universal Code for World-Class Success (Productivity Press, 2013).