SIST-TP ISO/TR 8550-1:2010

TECHNICAL ISO/TR
REPORT 8550-1
First edition
2007-06-01
Guidance on the selection and usage of
acceptance sampling systems for
inspection of discrete items in lots —
Part 1:
Acceptance sampling
Lignes directrices pour la sélection d'un système, d'un programme ou
d'un plan d'échantillonnage pour acceptation pour le contrôle d'unités
discrètes en lots —
Partie 1: Lignes directrices générales pour l'échantillonnage pour
acceptation
Reference number
©
ISO 2007
PDF disclaimer
This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but
shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In
downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat
accepts no liability in this area.
Adobe is a trademark of Adobe Systems Incorporated.
Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation
parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In
the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.

©  ISO 2007
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or
ISO's member body in the country of the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2007 – All rights reserved

Contents Page
Foreword. iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions. 2
4 Abuses and uses of acceptance sampling . 2
5 Acceptance sampling plans, schemes and systems. 5
6 Practical and economic advantages of using standard sampling plans. 5
7 Attributes versus variables. 7
8 Further considerations influencing a selection. 8
9 Making a comparison of the methods for sampling inspection . 23
10 Other methods sometimes adopted in practice . 29
11 Relevance of market and production conditions . 31
12 The final selection — Realism . 32
Annex A (informative) Example of a simple model for profit maximization under destructive
inspection by attributes . 33
Bibliography . 37

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 committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
In exceptional circumstances, when a technical committee has collected data of a different kind from that
which is normally published as an International Standard (“state of the art”, for example), it may decide by a
simple majority vote of its participating members to publish a Technical Report. A Technical Report is entirely
informative in nature and does not have to be reviewed until the data it provides are considered to be no
longer valid or useful.
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.
ISO/TR 8550-1 was prepared by Technical Committee ISO/TC 69, Applications of statistical methods,
Subcommittee SC 5, Acceptance sampling.
This first edition of ISO/TR 8550-1, together with ISO/TR 8550-2 and ISO/TR 8550-3, cancels and replaces
ISO/TR 8550:1994.
ISO/TR 8550 consists of the following parts, under the general title Guidance on the selection and usage of
acceptance sampling systems for inspection of discrete items in lots:
⎯ Part 1: Acceptance sampling
⎯ Part 3: Sampling by variables
The following part is under preparation:
⎯ Part 2: Sampling by attributes

iv © ISO 2007 – All rights reserved

Introduction
This part of ISO/TR 8550 gives guidance on the selection of an appropriate acceptance sampling scheme for
the inspection of discrete items submitted in lots from the schemes described in various national and
international standards.
There are many situations where products (materials, parts, components, assemblies and systems) are
transferred from one organization to another, where the organizations may be different companies or parts of
a single company or even different shops within a plant. In these situations both the supplier and the customer
may use acceptance sampling procedures to satisfy themselves that the product is of acceptable quality.
Suppliers will be seeking to maintain a reputation for good quality and to reduce the likelihood of claims under
warranty, but without incurring unnecessary production and supply costs. On the other hand, customers will
require adequate evidence, at minimum cost to themselves, that the product they receive conforms to
specifications. Compared with, say, 100 % inspection, suitable sampling methods will often be beneficial in
achieving these aims. Sometimes acceptance sampling methods are the only practical procedure, especially
when the tests for conformance are destructive.
Several types of sampling systems, schemes and plans are available for these purposes. They are presented
in a number of ISO Standards that explain how they are to be used. However, it is often difficult to decide on
the most appropriate procedure for use in a particular situation. The purpose of this part of ISO/TR 8550 is to
assist in that decision.
The choice of sampling system, scheme or plan depends on a number of conditions and on the prevailing
circumstances. In any supply situation, the first essential is that the supplier and the customer understand,
and have agreed upon, the requirements and the basis for release and acceptance of the product, including
any acceptance sampling methods to be used.
Lots that are non-acceptable cause difficulties for both supplier and customer. The supplier incurs additional
costs in rework, scrap, increased inspection, damage to reputation and possibly loss of sales. Delays in
delivery and re-inspection costs are a burden to the customer. For these reasons, it is usually considered
essential for the supplier to provide lots that have a very high probability of being accepted, i.e. 95 % or more.
The supplier has to ensure that quality control of the production or delivery process provides lots of a quality
sufficient to meet this objective. A basic principle of some acceptance sampling inspection schemes is to
promote the production of lots of acceptable quality. The primary purpose of these schemes is not to
discriminate between acceptable and non-acceptable lots, i.e. to sort, but to keep production under control to
yield an acceptable process average quality. Although all acceptance sampling plans are discriminatory to
some degree, the process average quality (expressed in terms of percent nonconforming or number of
nonconformities) should not be greater than half the acceptance quality limit in order to ensure a very high
probability of acceptance.
The primary purpose of the ISO/TR 8550 series is to give guidance on the selection of an acceptance
sampling system, scheme or plan. It does this principally by reviewing the available systems specified by
various standards and showing ways in which these can be compared in order to assess their suitability for an
intended application. The guide also indicates how prior knowledge of the manufacturing or service delivery
process and quality performance might influence the choice of sampling system, scheme or plan, and likewise
how the particular needs of the customer affect selection. Some specific circumstances encountered in
practice are described and the method of choosing a plan is explained. Some checklists or pointers and tables
are provided to assist users in selecting an appropriate system, scheme or plan for their purposes. Charts are
included to illustrate the procedures to be followed in the selection process.
This publication does not purport to include all the necessary provisions of a contract. Users are responsible
for its correct application.
TECHNICAL REPORT ISO/TR 8550-1:2007(E)

Guidance on the selection and usage of acceptance sampling
systems for inspection of discrete items in lots —
Part 1:
Acceptance sampling
1 Scope
This part of ISO/TR 8550 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. (For more detailed information about specific acceptance sampling systems, see
ISO/TR 8550-2 for sampling by attributes or ISO/TR 8550-3 for sampling by variables.)
The guidance in this part of ISO/TR 8550 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:
a) end items, such as complete products or sub-assemblies;
b) components and raw materials;
c) services;
d) materials in process;
e) supplies in storage;
f) maintenance operations;
g) data or records;
h) administrative procedures.
Although this part of ISO/TR 8550 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.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition listed applies. For undated references, the latest edition of the referenced
document (including any amendment) applies.
ISO 3534-1, Statistics — Vocabulary and symbols — Part 1: General statistical terms and terms used in
probability
ISO 3534-2, Statistics — Vocabulary and symbols — Part 2: Applied statistics
ISO 9000, Quality management systems — Fundamentals and vocabulary
3 Terms and definitions
For the purposes of this part of ISO/TR 8550, the terms and definitions given in ISO 3534-1, ISO 3534-2 and
ISO 9000 apply.
4 Abuses and uses of acceptance sampling
4.1 Abuses of acceptance sampling
Acceptance sampling has become unpopular since the early 1980s. Some of the reasons for this (although
certainly not all) are well founded, so it is important to be able to distinguish those situations where
acceptance sampling should not be used from those where it may be appropriate.
The chief arguments used against the use of acceptance sampling are as follows.
a) When quality is generally very high, the sample sizes needed to detect a slip in quality are
uneconomically large.
b) Quality cannot be inspected into a product.
c) It is far better to establish a robust design and to implement comprehensive process controls than to try to
find and eliminate nonconforming items after manufacture.
d) Most acceptance sampling standards are index
...