Mistakes happen—you’ve probably made a few so far today. And that’s often unavoidable, as your mind and abilities—or the capabilities of machines performing work—can only go so while following the immutable laws of the universe. Those involved with quality inspection play the role of determining these mistakes have occurred so producers and others can navigate the chaos. The ISO 2859 series of standards, for the most part, aids acceptance sampling systems often used between producers and suppliers.
ISO 2859-4:2020 – Sampling Procedures For Inspection By Attributes – Part 4: Procedures For Assessment Of Declared Quality Levels, however, takes a somewhat different focus. This international standard provides guidance and rules to assist the user in accounting for the risks of incorrect conclusions during sampling procedures in an informed manner.
How ISO 2859-4:2020 Differs from Other Standards in the Series
The ISO 2859-1:1999, ISO 2859-2:2020, and ISO 2859-3:2005 acceptance sampling procedures are used as simple, pragmatic rules for deciding on product release by inspection used in bilateral agreements between two parties. Therefore, the procedures do not make reference to formally declared quality levels. ISO 2859-4:2020 emerged from the need for sampling procedures suitable for formal, systematic inspections like reviews, audits, or systematic tests. As noted in the Introduction of ISO 2859-4:2020:
“When performing such a formal inspection, it is necessary both for the inspecting authority and for the body subject to inspection to consider the risks of reaching an incorrect conclusion. These risks have to be accounted for explicitly in the design of review/auditing/testing procedures.”
Please note, that if you do need all parts of the ISO 2859 standard, you can get them together as the ISO 2859-Sampling Procedures for Inspection by Attributes Package, which comes with a 45% discount on list prices.
About ISO 2859-4:2020
The ISO 2859-4:2020 standard is used while inspecting a sample for the objective evidence of conformity to some declared quality level. The standard provides sampling plans corresponding to four levels of discriminatory ability (Levels I, II, III, and IV), and it gives the limiting quality ratio (LQR) of each sampling plan. For levels I-III, the sampling plans obtain a risk no more than 5% of contradicting a correct declared quality level. The standard considers two types of quality models for discrete items and populations: the conforming-nonconforming model and the nonconformities model.
The procedures of the standard are applicable to entities such as lots, process output, inventory, files, etc., that allow random samples of individual items to be taken from the population. The sampling plans detailed in ISO 2859-4:2020 are applicable to the inspection of a variety of targets, including (but not limited to) the following: end items, components and raw materials, operations, materials in process, supplies in storage, maintenance operations, data or records, administrative procedures, accounting procedures or accounting entries, and internal control procedures.
Generally, this document focuses on controlling type I error. Therefore, unlike the procedures of other ISO 2859 standards, its procedures are not applicable to acceptance assessment of lots.
Changes to ISO 2859-4:2020
ISO 2859-4:2020 was prepared by Technical Committee ISO/TC 69, Application of statistical methods, Subcommittee SC 5, Acceptance sampling. In revising the 2002 edition of the same international standard, it went through the following changes:
- The scope was widened from testing for the percentage of nonconforming items to testing for the percentage of nonconformities per item.
- The sampling and decision algorithm is more detailed and has been moved to an earlier position in the document to facilitate the operational use of the document.
- An LQR level 0 was introduced, which can be used when a large probability of erroneously contradicting a correctly declared quality level can be tolerated.
- Informative Annex B was added to explain the mathematical-statistical background, and to provide tables on quality ratios.
ISO 2859-4:2020 – Sampling Procedures For Inspection By Attributes – Part 4: Procedures For Assessment Of Declared Quality Levels is available on the ANSI Webstore.