BS ISO 2859-4:2020

What is ISO 2859‑4 about?  

ISO 2859‑4 establishes single sampling plans for conformance testing, i.e., for assessing whether the quality level of a relevant audit population (lot, process, inventory, file etc) conforms to a declared value. Sampling plans are provided corresponding to four levels of discriminatory ability. Each sampling plan's limiting quality ratio (LQR) is given for reference. The sampling plans have been devised for levels I-III to obtain a risk of no more than 5 % of contradicting a correct declared quality level. 

ISO 2859‑4 can be used for various forms of quality inspection in situations where objective evidence of conformity to some declared quality level is to be provided using inspection of a sample. The procedures apply to entities such as lots, process output, etc., allowing random samples of individual items to be taken from the entity. 

ISO 2859‑4 considers two types of quality models for discrete items and populations, as follows: 

• The conforming-nonconforming model, where each item is classified as conforming or nonconforming, and where the quality indicator of a population of items is the proportion p of nonconforming items, or, equivalently, the percentage 100 p of nonconforming items 
• The nonconformities model, where the number of nonconformities is counted on each item, and where the quality indicator of a population of items is the average number λ of nonconformities found on items in the population, or, equivalently, the percentage 100 λ of nonconformities on items in the population 

Who is ISO 2859‑4 for? 

ISO 2859‑4 on sampling procedures for inspection by attributes are useful for: 

• Auditors 
• Quality assurance teams 
• Research and development teams 

Why should you use ISO 2859‑4?  

The procedures in ISO 2859-1 to ISO 2859-3 are well suited for acceptance sampling purposes, but they should not be used in reviews, audits, systematic tests, etc. to verify a quality that has been declared for some entity. The main reason is that the procedures have been indexed in terms of quality levels that are relevant solely for the pragmatic purposes of acceptance sampling, and the various risks have been balanced accordingly in a pragmatic attitude. 

The procedures in ISO 2859‑4 have been developed as a response to the growing need for sampling procedures suitable for formal, systematic inspections such as reviews or audits or systematic tests.  ISO 2859‑4 provides you guidance and rules to assist in accounting for the risks of incorrect conclusions in an informed manner. The rules in ISO 2859‑4 have been devised such that there is only an acceptably small risk of contradicting the declared quality level when in fact the actual level conforms to the declared level. This allows you to obtain the benefit of a moderate sample size. 

What’s changed since the last update? 

BS ISO 2859‑4:2020 replaces ISO 2859-4:2002, which has been technically revised. The main changes compared to the previous edition are as follows: 

• The scope has been 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, so as to facilitate the operational use of the document 
• An LQR level 0 has been introduced, which can be used when a large probability of erroneously contradicting a correctly declared quality level can be tolerated 
• An informative Annex B has been added to explain the mathematical-statistical background, and to provide tables on quality ratios