Attribute Sampling Plans & Inspection by Variable Procedures | ASQ

Attribute & Variable Sampling Plans and Inspection Procedures

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ANSI/ASQ Z1.4: Sampling Procedures and Tables for Inspection by Attributes

In “Comparing Acceptance Sampling Standards, Part 1,” Dean V. Neubauer and Stephen N. Luko describe ANSI/ASQ Z1.4: Sampling Procedures and Tables for Inspection by Attributes as an American national standard with direct lineage to MIL-STD-105E, a military standard that describes the sampling procedures and tables for inspection by attributes. When the U.S. Department of Defense stopped supporting MIL-STD-105E in 1995, it recommended ANSI/ASQ Z1.4 as the replacement. 

The Z1.4 standard is similar in format to both MIL-STD-105E and ASTM E2234-09: Standard Practice for Sampling a Stream of Product by Attributes Indexed by AQL. However, it differs in its definition of what constitutes a rejectable item. Best used in-house and in domestic transactions, ANSI/ASQ Z1.4 employs definitions and terminology in accordance with ANSI/ASQ A3534-2:2006: Statistics—Vocabulary and Symbols—Part 2, Applied Statistics.  

The following two definitions are particularly important in applying the standard:

  • Defect: A departure of a quality characteristic from its intended level or state that occurs with a severity sufficient to cause an associated product or service not to satisfy intended normal, or foreseeable, usage requirements.
  • Nonconformity: A departure of a quality characteristic from its intended level or state that occurs with severity sufficient to cause an associated product or service not to meet a specification requirement.  

ANSI/ASQ Z1.4 presents acceptance sampling plans for attributes in terms of the percentage or proportion of product in a lot or batch that departs from some requirement. The general terminology used in the standard is given in terms of percentage of nonconforming units or number of nonconformities because these terms are likely to constitute the most widely used criteria for acceptance sampling.  

Revisions to the Z1.4 standard in 2013 addressed an error in a table heading and a typographical error in each of the following tables: VIII, X-D-1, X-H-1, and X-N-2.

ANSI/ASQ Z1.9: Sampling Procedures and Tables for Inspection by Variables for Percent Nonconforming

According to Neubauer and Luko’s “Comparing Acceptance Sampling Standards, Part 2,” ANSI/ASQ Z1.9: Sampling Procedures and Tables for Inspection by Variables for Percent Nonconforming represents an effort to unify variables and attributes sampling systems. 

The Z1.9 standard provides a reasonable match between a modified MIL-STD-414, offering sampling procedures and tables for inspection by variables and for percent defective, and MIL-STD-105. Other changes included making the inspection levels coincide between the two standards, adopting the switching rules and lot size ranges of MIL-STD-105, and making editorial changes as appropriate.

Given the lot size and acceptance quality limit (AQL), moving between the two standards with the same code letter and AQL is possible. The procedures and structure of ANSI/ASQ Z1.9 are essentially the same as for MIL-STD-414. The set of examples in MIL-STD-414 has been retained and leads the user through application of the Z1.9 standard.

The ANSI/ASQ Z1.9 standard is an excellent vehicle for in-house use and stands as the national standard to be employed internally in the United States.

Revisions in 2013 addressed a typographical error found in Table B-2.

Learn more about ANSI/ASQ Z1.4 & Z1.9

For a more comprehensive discussion of the Z1.4 and Z1.9 standards and their relation to the corresponding military, ASTM, and ISO standards, see the following resources:

Visit the Knowledge Center to find more resources related to Z1.4 and Z1.9.

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