ISO/TC 69/SC 5 - Acceptance sampling

This document 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. The limiting quality ratio (LQR) (see Clause 4) of each sampling plan is given for reference. For levels I-III, the sampling plans have been devised so as to obtain a risk no more than 5 % of contradicting a correct declared quality level. The risk of failing to contradict an incorrectly declared quality level which is related to the LQR is no more than 10 %. The sample sizes for level 0 are designed in a way that the LQR factors of the sampling plans are compatible with the LQR factors for level I. In contrast to the procedures in the other parts of the ISO 2859 series, the procedures in this document are not applicable to acceptance assessment of lots. Generally, this document mainly focuses on controlling type I error, which differs from the balancing of the risks in the procedures for acceptance sampling. This document 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 by means of inspection of a sample. The procedures are applicable to entities such as lots, process output, etc. that allow random samples of individual items to be taken from the entity. The sampling plans provided in this document are applicable, but not limited, to the inspection of a variety of targets such as: — 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; — internal control procedures. This document considers two types of quality models for discrete items and populations, as follows. i) 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. ii) 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.

This document specifies an acceptance sampling system for inspection by attributes indexed by limiting quality (LQ). The sampling system is used for lots in isolation (isolated sequences of lots, an isolated lot, a unique lot or a short series of lots), where switching rules, such as those of ISO 2859‑1, are not applicable. Inspection levels, as provided by ISO 2859‑1 to control the relative amount of inspection, are not provided in this document. In many industrial situations, in which switching rules might be used, they are not applied for a number of reasons, not all of which might be valid: a) production is intermittent (not continuous); b) production is from several different sources in varying quantities, i.e. "job lots"; c) lots are isolated; d) lots are resubmitted after inspection. The sampling plans in this document are indexed by a series of specified values of limiting quality (LQ), where the consumer's risk (the probability of acceptance at the LQ) is usually below 0,10 (10 %), except in some instances. This document is intended both for inspection for nonconforming items and for inspection for nonconformities per 100 items. It is intended to be used when the supplier and the consumer both regard the lot to be in isolation. That is, the lot is unique in that it is the only one of its type produced. It can also be used when there is a series of lots too short for switching rules to be applied.

This International Standard specifies sequential sampling plans and procedures for inspection by variables of discrete items. The plans are indexed in terms of producer's risk point and the consumer's risk point. Therefore, they are suitable not only for the purposes of acceptance sampling, but for the more general purpose of the testing of simple statistical hypotheses for proportions. The purpose of this International Standard is to provide procedures for the sequential assessment of inspection results that may be used to induce the supplier 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 a lot (or process) of poor quality. This International Standard is primarily designed for use under the following conditions: a) where the inspection procedure is to be applied to a continuing series of lots of discrete products all supplied by one producer using one production process. In such a case, sampling of particular lots is equivalent to the sampling of the process. If there are different producers or production processes, this International Standard shall be applied to each one separately; b) where only a single quality characteristic x of these products is taken into consideration, which must be measurable on a continuous scale; c) where the measurement error is negligible (i.e. with a standard deviation no more than 10 % of the process standard deviation); d) where production is stable (under statistical control) and the quality characteristic x has a known standard deviation, and is distributed according to a normal distribution or a close approximation to the normal distribution; CAUTION — The procedures in this International Standard are not suitable for application to lots that have been screened previously for nonconforming items. e) where a contract or standard defines an upper specification limit U, a lower specification limit L, or both; an item is qualified as conforming if and only if its measured quality characteristic, x, satisfies the appropriate one of the following inequalities: x ≤ U (i.e. the upper specification limit is not violated); x ≥ L (i.e. the lower specification limit is not violated); and (i.e. neither the upper nor the lower specification limit is violated.) Inequalities 1) and 2) are called cases with a "single specification limit", and 3) is the case with "double specification limits". In this International Standard, it is assumed that, where double specification limits apply, conformance to both specification limits is either equally important to the integrity of the product or is considered separately for both specification limits. In the first case, it is appropriate to control the combined percentage of product outside the two specification limits. This is referred to as combined control. In the second case, nonconformity beyond each of the limits is controlled separately, and this is referred to as separate control.

ISO 28594:2017 provides a set of accept‑zero sampling systems and procedures for planning and conducting inspections to assess quality and conformance to specified requirements. In addition, this International Standard provides requirements for alternative acceptance methods proposed by the supplier. Such alternative methods would be based upon establishing and implementing an internal prevention‑based quality management system as a means of ensuring that all products conform to requirements specified by the contract and associated specifications and standards. ISO 28594:2017, when cited in contract, is applicable to the supplier and extends to subcontractors or vendors. The quality plans are to be applied as specified in the contract documents, and deliverables may be submitted for acceptance if the requirements of this International Standard have been met. Sampling systems and procedures in this International Standard are applicable, when appropriate, to assess conformance to requirements of the following: a) end items; b) components or basic materials; c) operations or services; d) materials in process; e) supplies in storage; f) maintenance operations; g) data or records; h) administrative procedures. NOTE Use of the word "product" throughout this International Standard also refers to services and other deliverables. The sampling systems and procedures of this International Standard are not intended for use with destructive tests or where product screening is not feasible or desirable. In such cases, the sampling systems to be used will be specified in the contract or product specifications.

ISO 28593:2017 specifies a system of single sampling schemes for lot-by-lot inspection by attributes. All the sampling plans of the present system are of accept-zero form, i.e. no lot is accepted if the sample from it contains one or more nonconforming items. The schemes depend on a suitably-defined average outgoing quality limit (AOQL), the value of which is chosen by the user; no restrictions are placed on the choice of the value of the AOQL or on the sizes of successive lots in the series. The methodology ensures that the overall average quality reaching the customer or market-place will not exceed the AOQL in the long run.

ISO 28591:2017 specifies 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. The purpose of this International Standard is to provide 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 28591:2017 provides sampling plans that are applicable, but not limited, to inspection in 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. ISO 28591:2017 contains sampling plans for inspection by attributes of discrete items. The sampling plans may be used when the extent of nonconformity is expressed either in terms of proportion (or percent) nonconforming items or in terms of nonconformities per item (per 100 items). The sampling plans are based on the assumption that nonconformities occur randomly and with statistical independence. There may be good reasons to suspect that one nonconformity in an item could be caused by a condition also likely to cause others. If so, it would be better to consider the items just as conforming or not, and ignore multiple nonconformities. The sampling plans from this International Standard 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.

ISO 28590:2017 provides a general introduction to acceptance sampling by attributes and provides a brief summary of the attribute sampling schemes and plans used in ISO 2859‑1, ISO 2859‑2, ISO 2859‑3, ISO 2859‑4 and ISO 2859‑5, which describe specific types of attribute sampling systems. It also provides guidance on the selection of the appropriate inspection system for use in a particular situation.

ISO 28592:2017 provides double sampling plans by attributes for the acceptance inspection of lots of discrete items. The plans are indexed by the producer's risk quality (PRQ) and the consumer's risk quality (CRQ) where the nominal producer's and consumer's risks are respectively either (5 %, 5 %), (5 %, 10 %) or (10 %, 10 %). Plans are provided for inspection for percent nonconforming and for inspection for nonconformities per 100 items. The lot is accepted if there are no nonconforming items (nonconformities) in the first random sample, and rejected if it contains two or more nonconforming items (nonconformities). If precisely one nonconforming item is found in the first sample, a second random sample is drawn; the lot is then accepted if the second sample contains no nonconforming items (nonconformities) and rejected otherwise. The objective of this International Standard is to provide procedures that enable lot disposition to be determined quickly and economically if quality is particularly good or bad. For intermediate quality, a second sample is drawn in order to be able to discriminate more reliably between acceptable and unacceptable lots. The two sample sizes are chosen to minimize the maximum expected sample size with respect to incoming quality subject to the nominal risks not being exceeded. Similarly, the plans may be used to test the hypothesis that a lot or process quality level is equal to the PRQ (i.e. acceptable) against the alternative hypothesis that the quality level is equal to the CRQ (i.e. unacceptable). The plans are preferable to single sampling plans where the cost of inspection is high, where the delay and uncertainty caused by the possible requirement for second samples is inconsequential and where a relatively large ratio of the consumer's risk quality to the producer's risk quality can be tolerated. The plans are suitable for isolated lots or for short series of lots, where the sum of the two sample sizes is no larger than about 10 % of the size of the lot. The plans are also suitable for continuing series of lots when lots that fail to satisfy the acceptance criteria are 100 % inspected and all nonconforming items replaced by conforming items; however, for continuing series of lots, consideration should also be given to using double sampling plans from ISO 2859‑1. The statistical theory underlying the plans, tables and figures is provided in Annex A.

ISO 28598-1:2017 provides guidelines specifying the organizational principles of acceptance sampling in situations where the contract or the legislation provides for successive inspection to be carried out by different parties: the supplier, the customer and/or a third party. These guidelines are designed for inspection of populations of any product supplied or delivered in discrete items in lots. They are applicable to - supplier inspection (final inspection, product certification upon supplier's request), - customer inspection (incoming inspection, audit inspection, acceptance sampling), - third-party inspection (certification of product, inspection and supervision for observance of International Standard requirements, quality inspection carried out at the supplier, and/or customer, request), where the quality levels and the lot acceptability criteria are specified unilaterally by the supplier or contractually by the supplier and the customer. These guidelines are also applicable to situations when only one sampling inspection is actually needed. NOTE Single sampling APP plans by attributes are given in ISO 28598‑2. The guidelines provided by this part of ISO 28598 may be applied in developing standards on acceptance sampling for standard inspection models, specific items or quality levels, as well as in developing contracts, specifications and instructions. In contractual use of the APP, the parties concerned should acknowledge in the contract that they approve of its principles (also by referring to the present guidelines). The parties may also provide for the use of the APP in disputes and arbitration.

ISO 28597:2017 specifies, for quality levels expressed as nonconforming items per million items, procedures for estimating the quality level of a single entity (e.g. a lot) and, when the production process is in statistical control, for estimating the process quality level based on evidence from several samples. Procedures are also specified for using this information when selecting a suitable sampling plan so as to verify that the quality level of a given lot does not exceed a stated limiting quality level (LQL). For the case where no prior sample data is available, guidance is given for presuming a process quality level in selecting a plan.

This part of ISO 28598 provides attributes sampling procedures and single sampling plans for successive independent inspections of the same lot conducted by the supplier, customer and/or a third party. This part of ISO 28598 addresses: - supplier inspection (final inspection, product certification upon supplier's request); - customer inspection (incoming inspection, surveillance, acceptance sampling); - third party inspection. This part of ISO 28598 may also be applicable when only one inspection is needed. A catalogue of single sampling plans is given, indexed by the normative quality limits (NQLs). This part of ISO 28598 provides sampling procedures for: - finished product; - components and discrete items; - operations; - discrete items and the processes that produce them; - data and records. Attributes sampling procedures are provided for inspection of an isolated lot or a continuing series of lots of a discrete product. These procedures are applicable when a normative quality limit (NQL) is given and expressed in terms of percent nonconforming or nonconformities per 100 items. This part of ISO 28598 provides a co-ordinated system of supplier, customer and third party acceptance sampling procedures. It is also applicable to the case where a supplier individually, or on agreement with a customer, in a contract, specifies a lot quality criterion expressed in terms of an NQL. In either case, it provides a coherent methodology for designating lots as satisfactory or unsatisfactory for shipment and proposed use.

ISO 3951-1:2013 specifies an acceptance sampling system of single sampling plans for inspection by variables. It is indexed in terms of the acceptance quality limit (AQL) and is designed for users who have simple requirements. (A more comprehensive and technical treatment is given in ISO 3951-2.) ISO 3951-1:2013 is complementary to ISO 2859-1. The objectives of the methods laid down in ISO 3951-1:2013 are to ensure that lots of acceptable quality have a high probability of acceptance and that the probability of not accepting inferior lots is as high as practicable. This is achieved by means of the switching rules, which provide the following: an automatic protection to the consumer (by means of a switch to tightened inspection or discontinuation of sampling inspection) should a deterioration in quality be detected; an incentive (at the discretion of the responsible authority) to reduce inspection costs (by means of a switch to a smaller sample size) should consistently good quality be achieved. In ISO 3951-1:2013, the acceptability of a lot is implicitly determined from an estimate of the percentage of nonconforming items in the process, based on a random sample of items from the lot. ISO 3951-1:2013 is intended for application to a continuing series of lots of discrete products all supplied by one producer using one production process. If there are different producers or production processes, ISO 3951-1:2013 is applied to each one separately. ISO 3951-1:2013 is intended for application to a single quality characteristic that is measurable on a continuous scale. For two or more such quality characteristics, see ISO 3951-2.

ISO 3951-2:2013 specifies an acceptance sampling system of single sampling plans for inspection by variables. It is indexed in terms of the acceptance quality limit (AQL) and is of a technical nature, aimed at users who are already familiar with sampling by variables or who have complicated requirements. (A more introductory treatment is given in ISO 3951-1.) The objectives of the methods laid down in ISO 3951-2:2013 are to ensure that lots of an acceptable quality have a high probability of acceptance and that the probability of not accepting inferior lots is as high as practicable. This is achieved by means of the switching rules, which provide the following: automatic protection to the consumer (by means of a switch to tightened inspection or discontinuation of sampling inspection) should a deterioration in quality be detected; an incentive (at the discretion of the responsible authority) to reduce inspection costs (by means of a switch to a smaller sample size) should consistently good quality be achieved. In ISO 3951-2:2013, the acceptability of a lot is either implicitly or explicitly determined from an estimate of the percentage of nonconforming items in the process, based on a random sample of items from the lot. ISO 3951-2:2013 is intended for application to a continuing series of lots of discrete products all supplied by one producer using one production process. If there are different producers or production processes, ISO 3951-2:2013 is applied to each one separately.

ISO 3951-4:2011 establishes sampling plans and procedures by variables that can be used to assess whether the quality level of an entity (lot, process, etc.) conforms to a declared value. The sampling plans have been devised so that their operating characteristic curves match those of the corresponding attributes plans in ISO 2859-4 as closely as possible, so that the choice between using sampling by attributes and sampling by variables is not influenced by attempts to increase the chance of accepting an incorrectly declared quality level. In this part of ISO 3951, there is a risk of between 1,4 % and 8,2 % of contradicting a correct declared quality level. The risk is 10 % of failing to contradict an incorrect declared quality level which is related to the limiting quality ratio. Sampling plans are provided corresponding to three levels of discriminatory ability, and for the cases of unknown and known process standard deviation. In contrast to the procedures in the other parts of ISO 3951, the procedures in ISO 3951-4:2011 are not applicable to acceptance assessment of lots. Generally, the balancing of the risks of reaching incorrect conclusions in assessment procedures will differ from the balancing in the procedures for acceptance sampling. ISO 3951-4:2011 may be used for various forms of quality inspection in situations where objective evidence of conformity to some declared quality level is to be provided by means of inspection of a sample. The procedures are applicable to entities such as lots, process output, etc. that allow random samples of individual items to be taken from the entity. The sampling plans provided are applicable, but not limited, to inspection of a variety of products such as: end items; components and raw materials; operations; materials in process; supplies in storage; maintenance operations; data or records; administrative procedures. The procedures are intended to be used when the quality characteristics are measurable variables that are independent and normally distributed, and where the quantity of interest is the fraction of items that are nonconforming.

ISO 24153:2009 defines procedures for random sampling and randomization. Several methods are provided, including approaches based on mechanical devices, tables of random numbers, and portable computer algorithms. ISO 24153:2009 is applicable whenever a regulation, contract, or other standard requires random sampling or randomization to be used. The methods are applicable to such situations as a) acceptance sampling of discrete units presented for inspection in lots, b) sampling for survey purposes, c) auditing of quality management system results, and d) selecting experimental units, allocating treatments to them, and determining evaluation order in the conduct of designed experiments. Information is also included to facilitate auditing or other external review of random sampling or randomization results where this is required by quality management personnel or regulatory bodies. ISO 24153:2009 does not provide guidance as to the appropriate random sampling or randomization procedures to be used for any particular experimental situation or give guidance with respect to possible sampling strategy selection or sample size determination. Other ISO International Standards (such as ISO 2859, ISO 3951, ISO 8422, ISO 8423, ISO 13448, ISO 14560, ISO 18414, ISO 21247 and ISO 11648) or authoritative references should be consulted for guidance in such areas.

ISO/TR 8550-2:2007 provides guidance for acceptance sampling of products that are supplied in lots and that can be classified as consisting of discrete items (i.e. discrete articles of product). Each item in a lot can be identified and segregated from the other items in the lot and has an equal chance of being included in the sample. Each item of product is countable and has specific characteristics that are measurable or classifiable as being conforming or nonconforming (to a given specification). Standards on acceptance sampling by attributes are applicable to a wide variety of inspection situations. These include, but are not limited to, the following: end items, such as complete products or sub-assemblies; components and raw materials; services; materials in process; supplies in storage; maintenance operations; data or records; administrative procedures. Although ISO/TR 8550-2:2007 is written principally in terms of manufacture and production, it is applicable to the selection of sampling systems, schemes and plans for all types of product and processes as defined in ISO 9000.

ISO/TR 8550-3:2007 provides guidance for acceptance sampling of products that are supplied in lots and that can be classified as consisting of discrete items (i.e. discrete articles of product). Each item in a lot can be identified and segregated from the other items in the lot and has an equal chance of being included in the sample. Each item of product is countable and has specific characteristics that are measurable on a continuous scale. Each characteristic has, at least to a good approximation, a normal distribution or a distribution that can be transformed so that it closely resembles a normal distribution. Standards on acceptance sampling by variables are applicable to a wide variety of inspection situations. These include, but are not limited to, the following: end items, such as complete products or sub-assemblies; components and raw materials; services; materials in process; supplies in storage; maintenance operations; data or records; administrative procedures. Although ISO/TR 8550-3:2007 is written principally in terms of manufacture and production, it should be interpreted liberally as it is applicable to the selection of sampling systems, schemes and plans for all types of product and processes as defined in ISO 9000.

ISO TR 8550-1:2007 gives general guidance on the selection of an acceptance sampling system, scheme or plan. It does this principally in the context of standards that either already exist or are presently under development. The guidance is confined to acceptance sampling of products that are supplied in lots and that can be classified as consisting of discrete items (i.e. discrete articles of product). It is assumed that each item in a lot can be identified and segregated from the other items in the lot and has an equal chance of being included in the sample. Each item of product is countable and has specific characteristics that are measurable or classifiable as being conforming or nonconforming (to a given product specification). Standards on acceptance sampling are typically generic, as a result of which they can be applied to a wide variety of inspection situations. These include, but are not limited to, the following: end items, such as complete products or sub-assemblies; components and raw materials; services; materials in process; supplies in storage; maintenance operations; data or records; and administrative procedures. Although ISO TR 8550-1:2007 is written principally in terms of manufacture and production, this should be interpreted liberally, as it is applicable to the selection of sampling systems, schemes and plans for all types of products and processes as defined in ISO 9000.

ISO 3951-3:2007 specifies an acceptance sampling system of double sampling schemes for inspection by variables for percent nonconforming. It is indexed in terms of the acceptance quality limit (AQL). The objectives of the methods laid down in ISO 3951-3:2007 are to ensure that lots of acceptable quality have a high probability of acceptance and that the probability of non-accepting inferior lots is as high as practicable. This is achieved by means of the switching rules, which provide automatic protection to the consumer (by means of a switch to tightened inspection or discontinuation of sampling inspection) should a deterioration in quality be detected, and an incentive (at the discretion of the responsible authority) to reduce inspection costs (by means of a switch to a smaller sample size) should consistently good quality be achieved. In ISO 3951-3:2007, the acceptability of a lot is implicitly or explicitly determined from an estimate of the percentage of nonconforming items in the process, based on either one or two random samples of items from the lot. ISO 3951-3:2007 is primarily designed for use under the following conditions: where the inspection procedure is to be applied to a continuing series of lots of discrete products all supplied by one producer using one production process; where the items of product have a single quality characteristic; where the quality characteristic is measurable on a continuous scale; where the measurement error is negligible (i.e. with a standard deviation no more than 10 % of the corresponding process standard deviation); where production is stable (under statistical control) and the quality characteristic is distributed, at least to a close approximation, according to a normal distribution; where the possibility of having to select and inspect a second sample is administratively acceptable; and where a contract or standard defines an upper specification limit, a lower specification limit, or both on the quality characteristic. The procedures in ISO 3951-3:2007 are not suitable for application to lots that have been screened previously for nonconforming items.

ISO 3951-5:2006 specifies a system of sequential sampling plans (schemes) for lot-by-lot inspection by variables. The schemes are indexed in terms of a preferred series of acceptance quality limit (AQL) values, ranging from 0,01 to 10, which are defined in terms of percent nonconforming items. The schemes are designed to be applied to a continuing series of lots. ISO 3951-5:2006 is designed for use under the following conditions: where the inspection procedure is to be applied to a continuing series of lots of discrete products all supplied by one producer using one production process; where only a single quality characteristic of these products is taken into consideration, which must be measurable on a continuous scale; where the uncertainty of the measurement system is negligible with respect to the production process standard deviation; where production is stable (under statistical control) and the quality characteristic is distributed according to a normal distribution (or a close approximation to the normal distribution) or a distribution which may be mathematically transformed to a normal distribution; where the standard deviation of the quality characteristic is known; and where a contract or standard defines an upper specification limit, a lower specification limit or both.

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 2859-3:2005 specifies generic skip-lot sampling procedures for acceptance inspection by attributes. The purpose of these procedures is to provide a way of reducing the inspection effort on products of high quality submitted by a supplier who has a satisfactory quality assurance system and effective quality controls. The reduction in inspection effort is achieved by determining at random, with a specified probability, whether a lot presented for inspection will be accepted without inspection. This procedure extends the principle of the random selection of sample items already applied in ISO 2859-1 to the random selection of lots. The skip-lot sampling procedures specified in ISO 2859-3:2005 are applicable to, but not limited to, inspection of end items, such as complete products or sub-assemblies, components and raw materials, and materials in process.

ISO 11648-1:2002 establishes the general principles for the application and statistical treatment of the sampling of bulk materials. It also provides general guidance and examples for estimating necessary variances and checking precision and bias when the average value of a quality characteristic is investigated. Furthermore, this part of ISO 11648-1:2002 gives information relating to the statistical analyses of serial data, by the use of variograms and correlograms. ISO 11648-1:2002 also defines the basic terms with definitions for the sampling of bulk materials. These terms are necessary for providing a better understanding of sampling techniques as well as making it easier to fulfil requirements.

ISO 28801:2011 provides double sampling plans by attributes for the acceptance inspection of lots of discrete items. The plans are indexed by the producer's risk quality (PRQ) and the consumer's risk quality (CRQ) where the nominal producer's and consumer's risks are respectively either (5 %, 5 %), (5 %, 10 %) or (10 %, 10 %). Plans are provided for inspection for percent nonconforming and for inspection for nonconformities per 100 items. The lot is accepted if there are no nonconforming items (nonconformities) in the first random sample, and rejected if it contains two or more nonconforming items (nonconformities). If precisely one nonconforming item is found in the first sample, a second random sample is drawn; the lot is then accepted if the second sample contains no nonconforming items (nonconformities) and rejected otherwise. The objective of ISO 28801:2011 is to provide procedures that enable lot disposition to be determined quickly and economically if quality is particularly good or bad. For intermediate quality, a second sample is drawn in order to be able to discriminate more reliably between acceptable and unacceptable lots. The two sample sizes are chosen to minimize the maximum expected sample size with respect to incoming quality subject to the nominal risks not being exceeded. Similarly, the plans may be used to test the hypothesis that a lot or process quality level is equal to the PRQ (i.e. acceptable) against the alternative hypothesis that the quality level is equal to the CRQ (i.e. unacceptable). The plans are preferable to single sampling plans where the cost of inspection is high, where the delay and uncertainty caused by the possible requirement for second samples is inconsequential and where a relatively large ratio of the consumer's risk quality to the producer's risk quality can be tolerated. The plans are suitable for isolated lots or for short series of lots, where the sum of the two sample sizes is no larger than about 10 % of the size of the lot. The plans are also suitable for continuing series of lots when lots that fail to satisfy the acceptance criteria are 100 % inspected and all nonconforming items replaced by conforming items; however, for continuing series of lots, consideration should also be given to using double sampling plans from ISO 2859-1. The statistical theory underlying the plans, tables and figures is provided in Annex A.

ISO 8423:2008 specifies sequential sampling plans and procedures for inspection by variables of discrete items. The plans are indexed in terms of producer's risk point and the consumer's risk point. Therefore, they are suitable not only for the purposes of acceptance sampling, but for the more general purpose of the testing of simple statistical hypotheses for proportions. The purpose of ISO 8423:2008 is to provide procedures for the sequential assessment of inspection results that may be used to induce the supplier 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 a lot (or process) of poor quality. ISO 8423:2008 is primarily designed for use under the following conditions: where the inspection procedure is to be applied to a continuing series of lots of discrete products all supplied by one producer using one production process; where only a single quality characteristic of these products is taken into consideration, which must be measurable on a continuous scale; where the measurement error is negligible (i.e. with a standard deviation no more than 10 % of the process standard deviation); where production is stable (under statistical control) and the quality characteristic has a known standard deviation, and is distributed according to a normal distribution or a close approximation to the normal distribution; where a contract or standard defines an upper specification limit, a lower specification limit, or both. It is assumed that, where double specification limits apply, conformance to both specification limits is either equally important to the integrity of the product or is considered separately for both specification limits. The procedures in ISO 8423:2008 are not suitable for application to lots that have been screened previously for nonconforming items.

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.

ISO 2859-10:2006 provides a general introduction to acceptance sampling by attributes and provides a brief summary of the attribute sampling schemes and plans used in ISO 2859-1, ISO 2859-2, ISO 2859-3, ISO 2859-4 and ISO 2859-5, which describe specific types of attribute sampling systems. ISO 2859-10:2006 also provides guidance on the selection of the appropriate inspection system for use in a particular situation.

ISO 3951-2:2006 specifies an acceptance sampling system of single sampling plans for inspection by variables, indexed in terms of the Acceptance Quality Limit (AQL). ISO 3951-2:2006 is primarily designed for use under the following conditions: where the inspection procedure is to be applied to a continuing series of lots of discrete products all supplied by one producer using one production process; where the quality characteristics of the items of product are measurable on a continuous scale; where the measurement error is negligible (i.e. with a standard deviation no more than 10 % of the corresponding process standard deviation); where production is stable (under statistical control) and the quality characteristics are distributed, at least to a close approximation, according to normal distributions; where, in the case of multiple quality characteristics, the characteristics are independent of one another, at least approximately; where a contract or standard defines an upper specification limit, a lower specification limit, or both on each of the quality characteristics.

ISO 18414:2006 specifies a system of single sampling schemes for lot-by-lot inspection by attributes. All the sampling plans of the system are of accept-zero form, i.e. no lot is accepted if the sample from it contains one or more nonconforming items. The schemes depend on a suitably-defined average outgoing quality limit (AOQL), the value of which is chosen by the user; no restrictions are placed on the choice of the value of the AOQL or on the sizes of successive lots in the series. The methodology ensures that the overall average quality reaching the customer or market-place will not exceed the AOQL in the long run. ISO 18414:2006 is designed for use under the following conditions: 1) where the inspection procedure is to be applied to a series of lots of discrete items that are intended to be identical, and which are all supplied by one producer using one production process; 2) where one or more quality characteristics of these products are taken into consideration, which must all be classifiable as either conforming or nonconforming; 3) where the inspection error involved in classifying the state of a product's quality characteristic(s) is negligible; and 4) where inspection is non-destructive. ISO 18414:2006 can be suitable for regulatory purposes, as control of the expected quality of items reaching the market-place is achieved with the smallest possible sample sizes, and long-term control of the realized, or actual quality level in the market-place is achieved with certainty, regardless of how long or short individual suppliers' series may be. ISO 18414:2006 can be used by suppliers/producers, buyers/consumers and regulatory agencies to provide control of the expected quality of the totality of accepted product of each type from each source.

ISO 3951-1:2005 specifies an acceptance sampling system of single sampling plans for inspection by variables, in which the acceptability of a lot is implicitly determined from an estimate of the percentage of nonconforming items in the process, based on a random sample of items from the lot. ISO 3951-1:2005 is primarily designed for application under the following conditions: where the inspection procedure is to be applied to a continuing series of lots of discrete products all supplied by one producer using one production process; where only a single quality characteristic x of these products is taken into consideration, which must be measurable on a continuous scale; where the measurement error is negligible, i.e. with a standard deviation no more than 10% of the process standard deviation; where production is stable (under statistical control) and the quality characteristic x is distributed according to a normal distribution or a close approximation to the normal distribution; where a contract or standard defines an upper specification limit U, a lower specification limit L, or both; an item is qualified as conforming if and only if its measured quality characteristic x satisfies the appropriate one of the following inequalities: x greater than or equal to L (i.e. the lower specification limit is not violated); x less than or equal to U (i.e. the upper specification limit is not violated); x greater than or equal to L and x less than or equal to U (i.e. neither the lower nor the upper specification limit is violated). The first two inequalities are called cases with a single specification limit, and the third a case with double specification limits. If double specification limits apply, it is assumed in ISO 3951-1:2005 that conformance to both specification limits is equally important to the integrity of the product; in such cases it is appropriate to apply a single AQL to the combined percentage of product outside the two specification limits. This is referred to as combined control.

ISO 21247:2005 provides a set of accept-zero sampling systems and procedures for planning and conducting inspections to assess quality and conformance to specified requirements. In addition, ISO 21247:2005 provides requirements for alternative acceptance methods proposed by the supplier. Such alternative methods would be based upon establishing and implementing an internal prevention-based quality management system as a means of ensuring that all products conform to requirements specified by the contract and associated specifications and standards. ISO 21247:2005, when cited in contract, is applicable to the supplier and extends to subcontractors or vendors. The quality plans are to be applied as specified in the contract documents, and deliverables may be submitted for acceptance if the requirements of ISO 21247:2005 have been met. Sampling systems and procedures in ISO 21247:2005 are applicable, when appropriate, to assess conformance to requirements of end items; components or basic materials; operations or services; materials in process; supplies in storage; maintenance operations; data or records; administrative procedures The sampling systems and procedures of ISO 21247:2005 are not intended for use with destructive tests or where product screening is not feasible or desirable. In such cases, the sampling systems to be used will be specified in the contract or product specifications.

ISO 13448-1:2005 provides guidelines specifying the organizational principles of acceptance sampling in situations where the contract or the legislation provides for successive inspection to be carried out by different parties: the supplier, the customer and/or a third party. These guidelines are designed for inspection of populations of any product supplied or delivered in discrete items in lots. They are applicable to supplier inspection (final inspection, product certification upon supplier's request), customer inspection (incoming inspection, audit inspection, acceptance sampling), and third-party inspection (certification of product, inspection and supervision for observance of International Standard requirements, quality inspection carried out at the supplier, and/or customer, request), where the quality levels and the lot acceptability criteria are specified unilaterally by the supplier or contractually by the supplier and the customer. These guidelines are also applicable to situations when only one sampling inspection is actually needed. The guidelines provided can be applied in developing standards on acceptance sampling for standard inspection models, specific items or quality levels, as well as in developing contracts, specifications and instructions. In contractual use of the APP, the parties concerned should acknowledge in the contract that they approve of its principles (also by referring to the present guidelines). The parties may also provide for the use of the APP in disputes and arbitration.

ISO 13448-2:2004 provides attributes sampling procedures and single sampling plans for successive independent inspections of the same lot conducted by the supplier, consumer and/or a third party. ISO 13448-2:2004 addresses supplier inspection (final inspection, product certification upon supplier's request), consumer inspection (incoming inspection, surveillance, acceptance sampling), and third party inspection. ISO 13448-2:2004 may also be applicable when only one inspection is needed. A catalogue of single sampling plans is given, indexed by the normative quality limits (NQLs). ISO 13448-2:2004 provides sampling procedures for finished product, components and discrete items, operations; discrete items and the processes that produce them, and data and records. Attributes sampling procedures are provided for inspection of an isolated lot or a continuing series of lots of a discrete product. These procedures are applicable when a normative quality limit (NQL) is given expressed in terms of percent nonconforming or nonconformities per 100 items. ISO 13448-2:2004 provides a co-ordinated system of supplier, consumer and third party acceptance sampling procedures. It is also applicable to the case where a supplier individually, or on agreement with a consumer, in a contract, specifies a lot quality criterion expressed in terms of an NQL. In either case, it provides a coherent methodology for designating lots as satisfactory or unsatisfactory for shipment and proposed use.

ISO 14560:2004 specifies, for quality levels expressed as nonconforming items per million items, procedures for estimating the quality level of a single entity (e.g. a lot) and, when the production process is in statistical control, for estimating the process quality level based on evidence from several samples. Procedures are also specified for using this information when selecting a suitable sampling plan so as to verify that the quality level of a given lot does not exceed a stated limiting quality level (LQL). For the case where no prior sample data is available, guidance is given for presuming a process quality level in selecting a plan.

ISO 2859-4:2002 establishes the sampling plans and the procedures that can be used to assess whether the quality level of an entity (lot, process, etc) conforms to a declared value. The sampling plans have been devised so as to obtain a risk of less than 5 % of contradicting a correct declared quality level. The risk is 10 % of failing to contradict an incorrect declared quality level that is related to the limiting quality ratio. Sampling plans are provided corresponding to three levels of discriminatory ability. In contrast to the procedures in the other parts of ISO 2859, the procedures in ISO 2859-4:2002 are not applicable to acceptance assessment of lots. Generally, the balancing of the risks of reaching incorrect conclusions in assessment procedures will differ from the balancing in the procedures for acceptance sampling. ISO 2859-4:2002 may be used for various forms of quality inspection in situations where objective evidence of conformity to some declared quality level is to be provided by means of inspection of a sample. The procedures are applicable to entities such as lots, process output, etc. that allow random samples of individual items to be taken from the entity. The sampling plans provided in ISO 2859-4:2002 are applicable, but not limited, to inspection of a variety of products such as end items, components and raw materials, operations, materials in process, supplies in storage, maintenance operations, data or records, and administrative procedures. The procedures are primarily intended to be used when the quantity of interest is the number or fraction of nonconforming items, for which the inspected items are classified as conforming or nonconforming. With minor changes, the procedures may also be used when the quantity of interest is the number of nonconformities or number of nonconformities per item. The necessary changes are the replacement of the "number of nonconforming items" by the "number of nonconformities" and the replacement of the "percent nonconforming items" by the "nonconformities per 100 items".

Explains the terms used in acceptance sampling, describes the various schemes and plans, gives practical advice on sampling inspection and discusses some of the theoretical aspects. This edition cancels and replaces ISO 2859.

Describes the selection process, general considerations influencing a selection, making a comparison of the methods for sampling inspection, other methods sometimes adopted in practice, market and production conditions - effect on the selection process, the final selection. Is applicable to a wide variety of inspection situations including end items (e.g. complete products or sub-assemblies), components and raw materials, services, materials in process, supplies in storage, maintenance operations, data or records.

Amends values in table 1 and subclause C.2.3 and equations in subclauses 3.2.2.1 and 3.2.3.1.

Replaces the formula for p in subclause C.2.2, item b).

The specified plans apply to: end items, components and raw materials, operations, materials in process, supplies in storage, maintenance operations, data or records, administrative procedures. Annexes A, B and C form an integral part of this standard.

Applies if all of the following conditions are satisfied: a) inspected are continuing series of lots of discrete items supplied by one producer from one production process; b) only a single quality characteristic x is taken into consideration; c) production is stable and x has a known standard deviation; d) an upper or lower limit (or both) is defined.

The procedures specified are applicable to the inspection of: end items, components and raw materials, services, materials in process, supplies in storage, data or records, administrative procedures. Annexes A and B form an integral part of this standard. Annexes C and D are for information only.

Is complementary to ISO 2859. Object of the methods laid down is to ensure that lots of an acceptable quality have a high probability of acceptance and that the probability of rejection of inferior lots is as high as possible. To be used under the following conditions: inspection procedure to be applied to a continuous series of lots of discrete products supplied by one producer using one production process; only a single quality characteristic is considered which must be measurable on a continuous scale; production is stable and quality characteristic is distributed normally; a contract or standard defines an upper and/or a lower specification limit.