NF ISO 8422

ISO 2859-5:2005 contains sequential sampling schemes that supplement the ISO 2859-1 acceptance sampling system for inspection by attributes, whereby a supplier, through the economic and psychological pressure of lot non-acceptance, can maintain a process average at least as good as the specified acceptance quality limit, while at the same time provide an upper limit for the risk to the consumer of accepting the occasional poor lot. The sampling schemes defined in ISO 2859-5:2005 are applicable, but not limited, to the inspection of: end items, components and raw materials, operations, materials in process, supplies in storage, maintenance operations, data or records, and administrative procedures. These schemes are designed to be applied to a continuing series of lots, that is, a series long enough to permit the described switching rules to be applied. These switching rules provide: a) enhanced protection to the consumer (by means of tightened sampling inspection criteria or discontinuation of sampling inspection) should deterioration in quality occur; and b) an incentive, at the discretion of the responsible authority, to reduce inspection costs (by means of reduced sampling inspection criteria) should consistently good quality be demonstrated over time. The individual sampling plans are not designed to be applicable outside of the schemes in which they are presented. If lots are produced in isolation or in a series too short for ISO 2859-5:2005 to apply, the user is advised to consult ISO 2859-2 for appropriate sampling plans.

ISO 8422:2006 contains sequential sampling plans and procedures for inspection by attributes of discrete items. The plans are indexed in terms of the producer's risk point and the consumer's risk point. Therefore, they can be used not only for the purposes of acceptance sampling, but for a more general purpose of the verification of simple statistical hypotheses for proportions. ISO 8422:2006 provides procedures for sequential assessment of inspection results that may be used to induce the supplier, through the economic and psychological pressure of non-acceptance of lots of inferior quality, to supply lots of a quality having a high probability of acceptance. At the same time, the consumer is protected by a prescribed upper limit to the probability of accepting lots of poor quality. ISO 8422:2006 provides sampling plans that are applicable, but not limited, to inspection of different fields, such as: end items, components and raw materials, operations, materials in process, supplies in storage, maintenance operations, data or records, and administrative procedures. The sampling plans from ISO 8422:2006 should primarily be used for the analysis of samples taken from processes. For example, they may be used for the acceptance sampling of lots taken from a process that is under statistical control. However, they may also be used for the acceptance sampling of an isolated lot when its size is large, and the expected fraction nonconforming is small (significantly smaller than 10%). In the case of the acceptance sampling of continuing series of lots, the system of sequential sampling plans indexed by acceptance quality limit (AQL) for lot-by-lot inspection published in ISO 2859-5 should be applied.