This part of ISO 2859 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 of each sampling plan is given for reference. For levels I-III, 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 of failing to contradict an incorrectly declared quality level which is related to the limiting quality ratio (see Clause 4) 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 ISO 2859, the procedures in this part of ISO 2859 are not applicable to acceptance assessment of lots. Generally, this part mainly focuses on controlling of type I error, which differs from the balancing of the risks in the procedures for acceptance sampling. This part of ISO 2859 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 this part of ISO 2859 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. ISO 2859-4 considers two type of quality models for discrete items and populations thereof. 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.