ISO 2859-4 pdf free download
ISO 2859-4-2020 pdf free download.Sampling procedures for inspection by attributes – Part 4: Procedures for assessment of declared quality levels.
If the sample size exceeds the size of the entity under investigation, then all items of the entity shall be inspected.
EXAMPLE If. in the example considered in 4.1. the entity under investigation is the computer records of administrative transactions during five business days. and the number of transactions each day are approximately equal, then the total sample of n = 127 transactions are selected as five sub-samples, three consisting of 25 transactions and two consisting of 26 transactions, selected by simple random sampling from the transactions on each of the five days.
4.3 Decision objective
The audit population is considered as conforming if the population quality indicator (percentage of nonconforming units, or percentage of nonconformities per item, respectively) is smaller or equal to the DQL. Otherwise, the audit population is considered as nonconforming. The inspection objective shall decide on the conformance of the population by taking one of two mutually exclusive decisions:
I) rejection, i.e., contradict the quality declaration expressed by the DQL and classify the population as nonconforming; ii) non-rejection or acceptance, i.e., do not contradict the quality declaration expressed by the DQL and classify the population as conforming.
4.4 Decision by sampling
Each of the n items in the sample shall be inspected, and the total number d of nonconforming items or, respectively, of the nonconformities on items in the sample shall be determined.
— If d is less than or equal to the non-rejection number c, the decision is non-rejection, i.e., the declared quality level is not contradicted.
— If d exceeds the non-rejection number c, the decision is rejection, i.e., the declared quality level is contradicted.
EXAMPLE Assume that, in the situation considered by the Example in 4.J,, two or fewer nonconforming items are found in the sample of 127 items. Then the sample result does not contradict the DQL of 0.65 % nonconforming items. If three or more nonconforming items are found, the sample evidence contradicts the DQL.
4.5 Disposition of nonconforming items
Any nonconforming items or items exhibiting nonconformities found in the sample shall not be returned to the rest of the items unless the nonconforming items are brought to a conforming condition and applicable administrative rules are followed.
Examples for the use of the sampling and decision procedure in industrial practice are provided in Annex A.
5 Principles
Any assessment procedure based on sampling is subject to sampling risk, i.e., the risk of taking an erroneous decision due to the limited information conveyed by a sample. In the present context, there are two types of erroneous conclusions on an audit population:
a) rejection although the population is actually conforming, i.e., the population quality indicator (percentage of nonconforming units, or percentage of nonconformities per item, respectively) is actually smaller or equal to the DQL;
b) non-rejection although the population is actually nonconforming, i.e., the population quality indicator (percentage of nonconforming units, or percentage of nonconformities per item, respectively) is actually exceeding the DQL.
The corresponding error risks are expressed by the respective error probabilities, namely a) the probability of rejecting an actually conforming population; b) the probability of not rejecting an actually nonconforming population. The latter two risks shall be balanced by the design of the sampling plans.
The sampling plans for the LQR levels I, II and Ill are, with few exceptions for large DQLs, devised such
that the probability of contradicting an actually correct quality declaration is less than 5 %. For the
LQR level 0, the probability of contradicting an actually correct quality declaration is bounded by 20%.
See TableLZ through 5 for the detailed values.
For the inspection authority, it is vital to have a small probability of not detecting an incorrectly declared quality level. The design of the sampling plans In this document focusses on the limiting quality ratio (LQR): when the actual quality level is LQRXDQL, i.e., LQR times worse than the declared quality level DQL, the procedures in this document have a risk of less than 10 % of failing to contradict the declared quality level (corresponding to a 90 % probability of contradicting/rejecting the incorrect declared quality level).
The ideal LQR would be close to 1,00. The latter ideal case cannot be achieved with practically feasible sample sizes. This document considers four LQR levels 0, I, II and Ill. For all levels, the LQR values range between 4 and 13, roughly. The sample sizes for level 0 are set to make sure that level 0 has approximately the same LQR as level I at the same DQL value where the LQR ranges from 7,78 for the largest DQL up to 12,34 for the smallest DQL. Under the latter design, it is inevitable that under level 0 the probabilities of contradicting an actually correct quality declaration are considerably higher than under levels I, II, and Ill.
Technical details on the design of the sampling plans are provided in Annex B.
6 Declared quality level (DQL)
The DQL together with the LQR level is used for indexing the sampling plans provided in this document. The values of DQL in the tables are known as preferred DQLs. The series of preferred DQL values correspond to the series of preferred AQLs for inspection for nonconforming items given in ISO 2859-1.
There shall be a sound basis for the DQL used. The DQL shall not be deliberately overstated or understated.
When a DQL is designated for a certain type quality characteristic, it indicates that the supplier has good reason to believe that the quality is not worse than this designated value.
CAUTION — When the DQL is estimated from a sample taken from the entity of interest, the procedures in this document shall not be used. Such a verification of an estimate from a sample requires that the sample size and inspection result be taken into account in order to incorporate the uncertainty associated with the estimate. This uncertainty affects the assessment of the risks of making incorrect conclusions on the actual status of the entity of Interest. Such verification usually requires larger sample sizes than those used in the procedures described in this document.ISO 2859-4 pdf download.
