ISO 28593:2017

Acceptance sampling procedures by attributes — Accept-zero sampling system based on credit principle for controlling outgoing quality

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.

Procédures d'échantillonnage par attributs pour acceptation — Système d'échantillonnage de tolérance zéro-défaut basé sur le principe de crédit pour le contrôle de la qualité à la sortie

General Information

• Status: Published
• Publication Date: 22-Oct-2017
• ICS: 03.120.30 - Application of statistical methods
• Technical Committee: ISO/TC 69/SC 5 - Acceptance sampling
• Drafting Committee: ISO/TC 69/SC 5 - Acceptance sampling
• Current Stage: 9060 - Close of review
• Start Date: 03-Jun-2028

Relations

• Revises: ISO 18414:2006 - Acceptance sampling procedures by attributes — Accept-zero sampling system based on credit principle for controlling outgoing quality
• Effective Date: 04-Nov-2015

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 28593
First edition
2017-10
Acceptance sampling procedures by
attributes — Accept-zero sampling
system based on credit principle for
controlling outgoing quality
Procédures d'échantillonnage par attributs pour acceptation —
Système d'échantillonnage de tolérance zéro-défaut basé sur le
principe de crédit pour le contrôle de la qualité à la sortie
Reference number
ISO 28593:2017(E)
©
ISO 2017

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ISO 28593:2017(E)

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© ISO 2017, Published in Switzerland
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ii © ISO 2017 – All rights reserved

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ISO 28593:2017(E)

Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 2
3 Terms and definitions . 2
4 Symbols and abbreviated terms . 2
5 Average outgoing quality limit . 3
6 Credit principle . 3
7 Treatment of non-accepted lots . 4
8 Sampling plans . 4
9 Preliminary operations . 4
10 Standard procedure . 5
11 Procedure during continuing inspection . 6
12 Discontinuation of inspection . 6
Annex A (informative) Examples of sample sizes required for credit-based accept-zero plans .8
Bibliography . 9
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ISO 28593:2017(E)

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
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ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
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For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following
URL: www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 69, Applications of statistical methods,
Subcommittee SC 5, Acceptance sampling.
This first edition of ISO 28593 cancels and replaces ISO 18414:2006, of which it constitutes a minor
revision to change the reference number from 18414 to 28593.
With the view to achieve a more consistent portfolio, TC 69/SC 5 has simultaneously renumbered the
following standards, by means of minor revisions:
Old reference New reference Title
ISO 2859-10:2006 ISO 28590:2017 Sampling procedures for inspection by attributes — Intro-
duction to the ISO 2859 series of standards for sampling for
inspection by attributes
ISO 8422:2006 ISO 28591:2017 Sequential sampling plans for inspection by attributes
ISO 28801:2011 ISO 28592:2017 Double sampling plans by attributes with minimal sample
sizes, indexed by producer's risk quality (PRQ) and consumer's
risk quality (CRQ)
ISO 18414:2006 ISO 28593:2017 Acceptance sampling procedures by attributes — Accept-ze-
ro sampling system based on credit principle for controlling
outgoing quality
ISO 21247:2005 ISO 28594:2017 Combined accept-zero sampling systems and process control
procedures for product acceptance
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ISO 28593:2017(E)

ISO 14560:2004 ISO 28597:2017 Acceptance sampling procedures by attributes — Specified
quality levels in nonconforming items per million
ISO 13448-1:2005 ISO 28598-1:2017 Acceptance sampling procedures based on the allocation of
priorities principle (APP) — Part 1: Guidelines for the APP
approach
ISO 13448-2:2004 ISO 28598-2:2017 Acceptance sampling procedures based on the allocation of
priorities principle (APP) — Part 2: Coordinated single sam-
pling plans for acceptance sampling by attributes
Cross references between the above listed documents have been corrected in the minor revisions.
A list of all documents in the new ISO 28590 - ISO 28599 series of International Standards can be found
on the ISO website.
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INTERNATIONAL STANDARD ISO 28593:2017(E)
Acceptance sampling procedures by attributes — Accept-
zero sampling system based on credit principle for
controlling outgoing quality
1 Scope
1.1 This International Standard 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.
1.2 The schemes are intended to induce a supplier, through the economic and psychological pressure of
lot non-acceptance and consequent loss of accumulated credit, to attempt to maintain a nonconformity-
free process, while assuring, by means of the lowest practicable sample sizes, that the long-term
percentage of nonconforming items delivered to the customer or market-place does not exceed the
AOQL. This objective is achieved by a progressive reduction in the sample size in response to good quality
history.
1.3 The schemes are designed to be applied to a series of lots from each supplier. The credit principle
provides:
a) automatic protection to the customer if a deterioration in quality is detected, by means of a total
loss of accumulated credit and reversion to a relatively large sample size whenever a nonconforming
item is found, and 100 % inspection of
1) the first lot if it is not accepted, or
2) any non-accepted lot that immediately follows a non-accepted lot;
b) an incentive to reduce sampling costs (by means of a progressive reduction in required sample
size) if consistently good quality is achieved.
1.4 This International Standard is designed for use under the following conditions:
a) 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 (If there
are different producers or production processes, this International Standard is intended to be
applied to each one separately.);
b) where one or more quality characteristics of these products are taken into consideration, which
must all be classifiable as either conforming or nonconforming;
c) where the inspection error involved in classifying the state of a product's quality characteristic(s)
is negligible;
d) where inspection is non-destructive.
This International Standard 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. This International Standard can be used by
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ISO 28593:2017(E)

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.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 3534-2, Statistics — Vocabulary and symbols — Part 2: Applied statistics
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 3534-2 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at http://www.iso.org/obp
— IEC Electropedia: available at http://www.electropedia.org/
3.1
credit
K
total number of items accepted in a sequence of accepted lots since a lot in the
sequence was non-accepted, or since the start of inspection if all previous inspected lots have been
accepted
3.2
average outgoing quality
AOQ
long-term average quality level of outgoing product for a given value of incoming
product quality
Note 1 to entry: In this International Standard, the average outgoing quality (AOQ) is calculated over all accepted
lots together with the conforming items found after 100 % inspection of lots that are non-accepted when the
credit, K, is zero.
3.3
average outgoing quality limit
AOQL
a
maximum AOQ over all possible values of incoming product quality level for a
given acceptance sampling scheme
4 Symbols and abbreviated terms
The symbols and abbreviations used in this International Standard are as follows:
AOQ average outgoing quality, in percent nonconforming items
AOQL average outgoing quality limit, in percent nonconforming items
a specified value of the AOQL, expressed in proportion of nonconforming items
d number of nonconforming items in the sample
K credit (an integer)
K upper limit (if any) to the usable credit
max
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ISO 28593:2017(E)

n sample size
N lot size
5 Average outgoing quality limit
When the quality of lots submitted for inspection is very good, almost all the lots are accepted and
enter the market-place unchanged. The average outgoing quality (AOQ) of items to the market-place is
therefore a low percentage nonconforming.
When the quality of lots submitted for inspection is very poor, most of the lots are non-accepted and
100 % inspected. In this case, most of the items are subjected to inspection and only the conforming
items accepted, so the AOQ of items to the market-place is again a low percentage nonconforming, albeit
at a relatively high average inspection cost per item reaching the market-place.
As quality moves between these extremes, the AOQ increases, reaches a limit, and thereafter decreases.
The upper limit to the average outgoing percentage nonconforming is called the average outgoing
quality limit (AOQL). No sampling scheme obtained by use of this standard has an expected (or long-
term) AOQ in excess of the specified AOQL.
For an isolat
...