Zero Acceptance Sampling Plans to Reduce Inspection Costs

William A. Levinson

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Traditional ANSI/ASQ Z1.4 (formerly MIL-STD 105) sampling plans specify a sample size n and acceptance number c.  Double and multiple sampling plans reduce the average sample number (ASN) by accepting very good lots on the first sample, and similarly rejecting very bad lots.  Any ANSI/ASQ Z1.4 plan can however be converted into a zero acceptance number sampling plan (c=0 plan) that minimizes the amount of necessary inspection even further. Use of c=0 plans requires, however, that outgoing quality far exceed the specified acceptable quality level (AQL) due to the increased risk of rejecting lots at the AQL.

Learning Objectives:

Attendees will be able, upon completion of the webinar, be able to:

·         Define a traditional ANSI/ASQ Z1.4 sampling plan based on the inspection level, lot size (N), and acceptable quality level (AQL)

·         Calculate the producer's risk (alpha) at the AQL, and define the equivalent of a rejectable quality level (RQL) for which the consumer's risk (beta) is 10 percent. (ANSI/ASQ Z1.4 plans do not have formal RQLs but we treat, for analytical purposes, the nonconforming fraction at which the consumer's risk of acceptance is 10% as the RQL. The c=0 plan will therefore have a 10% or less chance of accepting the lot at this nonconforming fraction.)

·         Use ANSI/ASQ Z1.4's switching rules that require transitions between normal, tightened, and reduced inspections based on quality performance.

·         Define a zero acceptance (c=0) plan that provides the same level of protection at the rejectable quality level (RQL) of the ANSI/ASQ Z1.4 plan.

·         Construct the operating characteristic (OC) curve for the c=0 plan to allow customers to compare it to that of the original ANSI/ASQ Z1.4 plan.

·         Identify alternatives to c=0 plans that reduce the amount of necessary inspection in case the requirement that quality far exceed the AQL is not met.

 Please mention the Areas you will be touching during the Session: (Should have more than 6 bullet points)

Topics covered include:

·         Features of ANSI/ASQ Z1.4 including the inspection level, AQL, sample size n, and acceptance number c, along with the switching rules prescribed by the standard.

·         Producer's risk of rejecting a lot at the AQL

·         The operating characteristic (OC) curve, which reflects the chance of accepting a lot whose nonconforming fraction is p. This allows comparison of the c=0 plan to the traditional plan.

·         The c=0 plan as a form of discovery sampling, which calculates the necessary sample size (n) to be a certain percent—in this case, 90%--certain to detect at least one nonconformance if the problem is present at a certain level (in this case, the rejectable quality level).

·         The need for quality to far exceed the AQL due to the higher producer's risk of rejection of lots at the AQL by c=0 plans. Alternatives such as sequential sampling and narrow limit gauging, both of which reduce the amount of necessary inspection, are available when this requirement is not met.

Attendees will receive copies of the presentation slides and accompanying notes, along with spreadsheet versions of the two examples shown in the presentation. The spreadsheet includes the formulas for calculation of the RQL, calculation of the required sample size for the c=0 plan, and development of operating characteristic curves.

Benefits from training:

All manufacturing activities that use ANSI/ASQ Z1.4 (formerly MIL-STD 105)

Who will be benifited:

  • Quality Manager
  • manufacturing managers
  • engineers
  • technicians

Keywords of Topic can be used to trigger in some of the Search Engines and Social Media:

  • Sampling
  • inspection
  • attributes
  • ANSI/ASQ Z1.4
  • MIL-STD 105
  • zero acceptance sampling


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Speaker: William A. Levinson,

William A. Levinson, P.E., is the principal of Levinson Productivity Systems, P.C. He is an ASQ Fellow, Certified Quality Engineer, Quality Auditor, Quality Manager, Reliability Engineer, and Six Sigma Black Belt. He is also the author of numerous books on quality, productivity, and management.

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