Statistical methods in process management - Capability and performance - Part 1: General principles and concepts

ISO 22514-1:2009 describes the fundamental principles of capability and performance of manufacturing processes. It has been prepared to provide guidance about circumstances where a capability study is requested or is necessary to determine if the output from a manufacturing process or the production equipment (a production machine) is acceptable according to appropriate criteria. Such circumstances are common in quality control when the purpose for the study is part of some kind of production acceptance. These studies may also be used when diagnosis is required concerning a production output or as part of a problem solving effort. The methods are very versatile and have been applied for many situations.
ISO 22514-1:2009 is applicable to the following: organizations seeking confidence that their product characteristics requirements are fulfilled; organizations seeking confidence from their suppliers that their product specifications are and will be satisfied; those internal or external to the organization who audit it for conformity with the product requirements; those internal to the organization who deal with analysing and evaluating the existing production situation to identify areas for process improvement.

Méthodes statistiques dans la gestion de processus - Aptitude et performance - Partie 1: Principes et concepts généraux

L'ISO 22514-1:2009 décrit les principes fondamentaux de l'aptitude et de la performance des processus de fabrication. Elle a été élaborée pour fournir des recommandations concernant les circonstances dans lesquelles une étude d'aptitude est requise ou nécessaire pour déterminer si le résultat d'un processus de fabrication ou le matériel de production (une machine de fabrication) est acceptable selon des critères appropriés. Ces circonstances sont courantes dans le processus de contrôle de la qualité, lorsque l'objet de l'étude fait partie intégrante d'un certain type d'acceptation de la production. Ces études peuvent également être utilisées lorsqu'un diagnostic est requis concernant le rendement d'une production ou comme partie intégrante d'une démarche de résolution de problèmes. Les méthodes utilisées, très polyvalentes, ont été appliquées dans de nombreuses situations.
L'ISO 22514-1:2009 est applicable aux organismes qui cherchent à s'assurer que les exigences relatives aux caractéristiques de leurs produits sont satisfaites; aux organismes qui cherchent à s'assurer que leurs fournisseurs satisfont et satisferont aux spécifications de leurs produits; à ceux, en interne ou à l'extérieur de l'organisme, qui auditent ce dernier en termes de conformité aux exigences relatives au produit; à ceux, à l'intérieur de l'organisme, qui analysent et évaluent la situation de production existante pour identifier les secteurs d'amélioration du processus.

Statistične metode za obvladovanje procesov - Sposobnost in delovanje - 1. del: Splošna načela in pojmi

Ta del ISO 22514 opisuje temeljna načela sposobnosti in delovanja proizvodnih procesov. Pripravljen je bil z namenom nuditi vodilo o okoliščinah, kjer se zahteva študija sposobnosti oziroma je nujna za ugotavljanje, ali je rezultat proizvodnega procesa oziroma proizvodne opreme (proizvodnega stroja) sprejemljiv glede na ustrezna merila. Takšne okoliščine so običajne pri nadzoru kakovosti, kjer je namen študije del neke vrste prevzemanja proizvodnje. Te študije se lahko uporabljajo tudi, kadar se zahteva diagnoza glede proizvodnega rezultata ali kot del prizadevanj za reševanje problemov. Te metode so zelo vsestranske in so bile uporabljene za številne situacije. Ta del ISO 22514 velja za naslednje: organizacije, ki si prizadevajo za zaupanje, da so zahteve glede značilnosti njihovih proizvodov izpolnjene; organizacije, ki si prizadevajo za zaupanje njihovih dobaviteljev, da so in bodo njihove produktne specifikacije izpolnjene; tiste interne ali zunanje sodelavce organizacije, ki jo revidirajo glede skladnosti s produktnimi zahtevami; tiste interne ali zunanje sodelavce organizacije, ki opravljajo analize in vrednotenja obstoječih proizvodnih razmer za ugotavljanje področij za izboljšavo procesov.

General Information

Status
Withdrawn
Publication Date
03-Jun-2010
Withdrawal Date
19-Jan-2015
Technical Committee
Current Stage
9900 - Withdrawal (Adopted Project)
Start Date
16-Jan-2015
Due Date
08-Feb-2015
Completion Date
20-Jan-2015

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INTERNATIONAL ISO
STANDARD 22514-1
First edition
2009-10-01
Statistical methods in process
management — Capability and
performance —
Part 1:
General principles and concepts
Méthodes statistiques dans la gestion de processus — Aptitude et
performance —
Partie 1: Principes et concepts généraux

Reference number
©
ISO 2009
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 2009
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 2009 – All rights reserved

Contents Page
Foreword .iv
Introduction.v
1 Scope.1
2 Terms and definitions .1
2.1 Basic terms .1
2.2 Performance — Measures and indices .7
2.3 Capability — Measures and indices .10
3 Symbols, abbreviated terms and subscripts.13
3.1 Symbols and abbreviated terms .13
3.2 Subscripts .14
4 Pre-conditions for application .14
4.1 Aspects about establishing specifications.14
4.2 Distribution and sample size.15
4.3 Materials used in studies.15
4.4 Special circumstances.15
5 Collection of data .15
5.1 Traceability of data.15
5.2 Measurement uncertainty.16
5.3 Data recording .16
5.4 Outliers .16
6 Performance, capability and process analysis .16
6.1 Six different types of performance and capability.16
6.2 Basic considerations .17
6.3 Machine performance .19
6.4 Process performance and process capability.19
6.5 Position performance.20
6.6 Measurement system analysis.21
6.7 Performance and capability indices (PCIs).22
7 Results of use .22
8 Benefits of use.23
9 Limitations of use.23
Bibliography.24

iii
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.
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 22514-1 was prepared by Technical Committee ISO/TC 69, Applications of statistical methods,
Subcommittee SC 4, Applications of statistical methods in process management.
ISO 22514 consists of the following parts, under the general title Statistical methods in process
management — Capability and performance:
⎯ Part 1: General principles and concepts
⎯ Part 3: Machine performance studies for measured data on discrete parts
⎯ Part 4: Process capability estimates and performance measures [Technical Report]
The following parts are planned:
⎯ Part 5: Process capability statistics for attribute characteristics
⎯ Part 6: Process capability statistics for characteristics following a multivariate normal distribution
⎯ Part 7: Capability of measurement processes
It is planned to reissue ISO 21747, Statistical methods — Process performance and capability statistics for
measured quality characteristics, as part 2 of ISO 22514 in the future.
iv
Introduction
0.1 This introduction to capability treats the subjects “capability” and “performance” in a general way. To
fully understand the concepts, it would be helpful to consult ISO 22514-3, ISO/TR 22514-4 and ISO 21747.
These documents extend this introductory explanation to more specific uses of the procedures.
A process can either be a discrete process or a continuous process. A discrete process generates a sequence
of distinguishable items and a continuous process generates a continuous product (e.g. a lane of paper).
The purpose of a process is to manufacture a product or perform a service which satisfies a set of preset
specifications. The specifications for a process under investigation are defined for one or more characteristics
of the product or service. However, in process performance or capability, only one characteristic is considered
at a time. The characteristic can be measurable, countable or a property. The process thus generates either a
discrete or a continuous stochastic process.
⎯ The discrete process can be
⎯ a process of real numbers,
⎯ a process of natural numbers, or
⎯ a process telling which event from a set of events has occurred for the individual items.
As an example, the set of events for the individual items could be {colour acceptable; colour not
acceptable}.
In general, the notation for a discrete stochastic process is {X }, where X is the outcome of element i in
i i
the process. In the case where the characteristic is a property X , it is a value given to each of the events
i
in the set of events used for characterizing the process. For a discrete process, the index i is normally the
number of the item in the generated sequence of items. However, sometimes it may be more convenient
to use the time from a fixed point as the index.
⎯ When the process is continuous, a number of possibilities exist for the index, depending on the nature of
the product. When the product is e.g. a lane of paper, the index could be the length from a starting point
or it could be the time from a fixed point.
It should be noted that normally a serial correlation exists in a stochastic process.
A stochastic process is either stationary or non-stationary. The stringent definition of a stationary stochastic
process will not be given here. However, for a stationary process, a distribution exists for X which is
i
independent of i.
To obtain a process which satisfies the specifications, the stochastic process should be a stationary process
or a well-defined non-stationary process (e.g. a periodic process).
To evaluate a process, a performance study is performed. A performance study should, in fact, start as a
theoretical study of all the elements in the process before the process is physically implemented. When the
parameters of the various stages in the process have been analysed and redefined, the process is
implemented (this may be only as a test process).
Based on sampling from the implemented process, the numerical part of the performance study of the process
is started. A number of questions concerning the process must, beyond any reasonable doubt, be answered
correctly. The most important question to be answered is whether the process is a stationary process which is
v
stable or predictable for a reasonable period. For the process, it is then important to identify the probability
distribution of the process and to obtain estimates of the distribution parameters within a reasonable small
variance. Based on this information, the next stage in the performance study is to map the properties of the
characteristics under investigation and decide whether they are acceptable. If the properties cannot be
accepted, the parameters of the process itself must be changed in order to obtain a process with acceptable
properties.
Consider a well-defined and implemented process that has been accepted using a performance study. The
next stage for the process would then be to ensure that the parameters of the process and, thus, of the
stochastic process do not change, or change in a predicted way. This is performed by defining a suitable
capability study.
Studies of performance and capability indices are used more and more to assess production equipment, a
process, or even measurement equipment relative to specification criteria. Different types of studies are used
depending on the circumstances.
0.2 The concepts of performance and capability have been subject to large shifts of opinion. The most
fundamental shift has been to philosophically separate what is called “capability conditions” in this part of
ISO 22514-1 from “performance conditions”, the primary difference being whether statistical stability has been
obtained (capability) or not (performance). This naturally leads to the two sets of indices that are to be found in
2.2 and 2.3. It has become necessary to draw a firm distinction between these sets, since it has been
observed in industry that companies have been misled about their true capability position due to inappropriate
indices being calculated and published.

vi
INTERNATIONAL STANDARD ISO 22514-1:2009(E)

Statistical methods in process management — Capability and
performance —
Part 1:
General principles and concepts
1 Scope
This part of ISO 22514 describes the fundamental principles of capability and performance of manufacturing
processes. It has been prepared to provide guidance about circumstances where a capability study is
requested or is necessary to determine
...


SLOVENSKI STANDARD
01-julij-2010
6WDWLVWLþQHPHWRGH]DREYODGRYDQMHSURFHVRY6SRVREQRVWLQGHORYDQMHGHO
6SORãQDQDþHODLQSRMPL
Statistical methods in process management - Capability and performance - Part 1:
General principles and concepts
Méthodes statistiques dans la gestion de processus - Aptitude et performance - Partie 1:
Principes et concepts généraux
Ta slovenski standard je istoveten z: ISO 22514-1:2009
ICS:
03.120.30 8SRUDEDVWDWLVWLþQLKPHWRG Application of statistical
methods
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

INTERNATIONAL ISO
STANDARD 22514-1
First edition
2009-10-01
Statistical methods in process
management — Capability and
performance —
Part 1:
General principles and concepts
Méthodes statistiques dans la gestion de processus — Aptitude et
performance —
Partie 1: Principes et concepts généraux

Reference number
©
ISO 2009
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 2009
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 2009 – All rights reserved

Contents Page
Foreword .iv
Introduction.v
1 Scope.1
2 Terms and definitions .1
2.1 Basic terms .1
2.2 Performance — Measures and indices .7
2.3 Capability — Measures and indices .10
3 Symbols, abbreviated terms and subscripts.13
3.1 Symbols and abbreviated terms .13
3.2 Subscripts .14
4 Pre-conditions for application .14
4.1 Aspects about establishing specifications.14
4.2 Distribution and sample size.15
4.3 Materials used in studies.15
4.4 Special circumstances.15
5 Collection of data .15
5.1 Traceability of data.15
5.2 Measurement uncertainty.16
5.3 Data recording .16
5.4 Outliers .16
6 Performance, capability and process analysis .16
6.1 Six different types of performance and capability.16
6.2 Basic considerations .17
6.3 Machine performance .19
6.4 Process performance and process capability.19
6.5 Position performance.20
6.6 Measurement system analysis.21
6.7 Performance and capability indices (PCIs).22
7 Results of use .22
8 Benefits of use.23
9 Limitations of use.23
Bibliography.24

iii
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.
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 22514-1 was prepared by Technical Committee ISO/TC 69, Applications of statistical methods,
Subcommittee SC 4, Applications of statistical methods in process management.
ISO 22514 consists of the following parts, under the general title Statistical methods in process
management — Capability and performance:
⎯ Part 1: General principles and concepts
⎯ Part 3: Machine performance studies for measured data on discrete parts
⎯ Part 4: Process capability estimates and performance measures [Technical Report]
The following parts are planned:
⎯ Part 5: Process capability statistics for attribute characteristics
⎯ Part 6: Process capability statistics for characteristics following a multivariate normal distribution
⎯ Part 7: Capability of measurement processes
It is planned to reissue ISO 21747, Statistical methods — Process performance and capability statistics for
measured quality characteristics, as part 2 of ISO 22514 in the future.
iv
Introduction
0.1 This introduction to capability treats the subjects “capability” and “performance” in a general way. To
fully understand the concepts, it would be helpful to consult ISO 22514-3, ISO/TR 22514-4 and ISO 21747.
These documents extend this introductory explanation to more specific uses of the procedures.
A process can either be a discrete process or a continuous process. A discrete process generates a sequence
of distinguishable items and a continuous process generates a continuous product (e.g. a lane of paper).
The purpose of a process is to manufacture a product or perform a service which satisfies a set of preset
specifications. The specifications for a process under investigation are defined for one or more characteristics
of the product or service. However, in process performance or capability, only one characteristic is considered
at a time. The characteristic can be measurable, countable or a property. The process thus generates either a
discrete or a continuous stochastic process.
⎯ The discrete process can be
⎯ a process of real numbers,
⎯ a process of natural numbers, or
⎯ a process telling which event from a set of events has occurred for the individual items.
As an example, the set of events for the individual items could be {colour acceptable; colour not
acceptable}.
In general, the notation for a discrete stochastic process is {X }, where X is the outcome of element i in
i i
the process. In the case where the characteristic is a property X , it is a value given to each of the events
i
in the set of events used for characterizing the process. For a discrete process, the index i is normally the
number of the item in the generated sequence of items. However, sometimes it may be more convenient
to use the time from a fixed point as the index.
⎯ When the process is continuous, a number of possibilities exist for the index, depending on the nature of
the product. When the product is e.g. a lane of paper, the index could be the length from a starting point
or it could be the time from a fixed point.
It should be noted that normally a serial correlation exists in a stochastic process.
A stochastic process is either stationary or non-stationary. The stringent definition of a stationary stochastic
process will not be given here. However, for a stationary process, a distribution exists for X which is
i
independent of i.
To obtain a process which satisfies the specifications, the stochastic process should be a stationary process
or a well-defined non-stationary process (e.g. a periodic process).
To evaluate a process, a performance study is performed. A performance study should, in fact, start as a
theoretical study of all the elements in the process before the process is physically implemented. When the
parameters of the various stages in the process have been analysed and redefined, the process is
implemented (this may be only as a test process).
Based on sampling from the implemented process, the numerical part of the performance study of the process
is started. A number of questions concerning the process must, beyond any reasonable doubt, be answered
correctly. The most important question to be answered is whether the process is a stationary process which is
v
stable or predictable for a reasonable period. For the process, it is then important to identify the probability
distribution of the process and to obtain estimates of the distribution parameters within a reasonable small
variance. Based on this information, the next stage in the performance study is to map the properties of the
characteristics under investigation and decide whether they are acceptable. If the properties cannot be
accepted, the parameters of the process itself must be changed in order to obtain a process with acceptable
properties.
Consider a well-defined and implemented process that has been accepted using a performance study. The
next stage for the process would then be to ensure that the parameters of the process and, thus, of the
stochastic process do not change, or change in a predicted way. This is performed by defining a suitable
capability study.
Studies of performance and capability indices are used more and more to assess production equipment, a
process, or even measurement equipment relative to specification criteria. Different types of studies are used
depending on the circumstances.
0.2 The concepts of performance and capability have been subject to large shifts of opinion. The most
fundamental shift has been to philosophically separate what is called “capability conditions” in this part of
ISO 22514-1 from “performance conditions”, the primary
...


NORME ISO
INTERNATIONALE 22514-1
Première édition
2009-10-01
Méthodes statistiques dans la gestion de
processus — Aptitude et performance —
Partie 1:
Principes et concepts généraux
Statistical methods in process management — Capability and
performance —
Part 1: General principles and concepts

Numéro de référence
©
ISO 2009
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©  ISO 2009
Droits de reproduction réservés. Sauf prescription différente, aucune partie de cette publication ne peut être reproduite ni utilisée sous
quelque forme que ce soit et par aucun procédé, électronique ou mécanique, y compris la photocopie et les microfilms, sans l'accord écrit
de l'ISO à l'adresse ci-après ou du comité membre de l'ISO dans le pays du demandeur.
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
Publié en Suisse
ii © ISO 2009 – Tous droits réservés

Sommaire Page
Avant-propos .iv
Introduction.v
1 Domaine d'application .1
2 Termes et définitions .1
2.1 Termes fondamentaux .1
2.2 Performance — Mesures et indices.7
2.3 Aptitude — Mesures et indices .10
3 Symboles, termes abrégés et indices .13
3.1 Symboles et termes abrégés.13
3.2 Indices .14
4 Conditions préalables à l'application.14
4.1 Aspects relatifs à la détermination des spécifications .14
4.2 Distribution et effectif d'échantillon .15
4.3 Équipements utilisés dans les études .15
4.4 Circonstances particulières .15
5 Collecte des données.15
5.1 Traçabilité des données.15
5.2 Incertitude de mesure .16
5.3 Enregistrement des données .16
5.4 Valeurs aberrantes .16
6 Analyse de la performance, de l'aptitude et du processus.16
6.1 Six types différents de performance et d'aptitude.16
6.2 Éléments de base pris en considération.17
6.3 Performance de la machine.19
6.4 Performance du processus et aptitude du processus .19
6.5 Performance de position .20
6.6 Analyse du système de mesure.21
6.7 Indices de performance et d'aptitude (PCI) .22
7 Résultats de l'utilisation des indices.22
8 Avantages de l'utilisation des indices.23
9 Limites d'utilisation.23
Bibliographie.24

Avant-propos
L'ISO (Organisation internationale de normalisation) est une fédération mondiale d'organismes nationaux de
normalisation (comités membres de l'ISO). L'élaboration des Normes internationales est en général confiée
aux comités techniques de l'ISO. Chaque comité membre intéressé par une étude a le droit de faire partie du
comité technique créé à cet effet. Les organisations internationales, gouvernementales et non
gouvernementales, en liaison avec l'ISO participent également aux travaux. L'ISO collabore étroitement avec
la Commission électrotechnique internationale (CEI) en ce qui concerne la normalisation électrotechnique.
Les Normes internationales sont rédigées conformément aux règles données dans les Directives ISO/CEI,
Partie 2.
La tâche principale des comités techniques est d'élaborer les Normes internationales. Les projets de Normes
internationales adoptés par les comités techniques sont soumis aux comités membres pour vote. Leur
publication comme Normes internationales requiert l'approbation de 75 % au moins des comités membres
votants.
L'attention est appelée sur le fait que certains des éléments du présent document peuvent faire l'objet de
droits de propriété intellectuelle ou de droits analogues. L'ISO ne saurait être tenue pour responsable de ne
pas avoir identifié de tels droits de propriété et averti de leur existence.
L'ISO 22514-1 a été élaborée par le comité technique ISO/TC 69, Application des méthodes statistiques,
sous-comité SC 4, Application de méthodes statistiques au management de processus.
L'ISO 22514 comprend les parties suivantes, présentées sous le titre général Méthodes statistiques dans la
gestion de processus — Aptitude et performance:
⎯ Partie 1: Principes et concepts généraux
⎯ Partie 3: Études de performance de machines pour des données mesurées sur des parties discrètes
⎯ Partie 4: Estimations de l'aptitude de processus et mesures de performance [Rapport technique]
Les parties suivantes sont prévues:
⎯ Partie 5: Statistiques d'aptitude d’un processus pour les caractéristiques d’attribut
⎯ Partie 6: Statistiques de capacité opérationnelle d'un processus pour les caractéristiques qui suivent une
distribution normale à plusieurs variables
⎯ Partie 7: Aptitude des processus de mesure
Il est prévu de republier ultérieurement l'ISO 21747, Méthodes statistiques — Performances de processus et
statistiques d'aptitude pour les caractéristiques de qualité mesurées, en tant que partie 2 de l'ISO 22514.
iv © ISO 2009 – Tous droits réservés

Introduction
0.1 La présente introduction au concept de l'aptitude traite de l'«aptitude» et de la «performance» de
manière générale. La consultation des ISO 22514-3, ISO/TR 22514-4 et ISO 21747 se révèlerait utile pour
appréhender pleinement ces concepts. Ces documents étendent le présent exposé introductif à des
utilisations plus spécifiques des procédures.
Un processus peut être discontinu ou continu. Un processus discontinu génère une séquence d'individus
différenciables tandis qu'un processus continu génère un produit continu (par exemple une bobine de papier).
Un processus a pour objet de fabriquer un produit ou d'exécuter un service, qui satisfait à un ensemble de
spécifications préétablies. Les spécifications relatives au processus étudié sont définies pour une ou plusieurs
caractéristiques du produit ou du service. Les performances ou l'aptitude d'un processus ne tiennent toutefois
compte que d'une seule caractéristique à la fois. Cette caractéristique peut être mesurable, dénombrable ou
être une propriété. Le processus génère ainsi un processus stochastique discontinu ou continu.
⎯ Le processus discontinu peut être
⎯ un processus de nombres réels,
⎯ un processus de nombres naturels, ou
⎯ un processus qui indique l'occurrence d'un événement donné issu d'un ensemble d'événements pour
les individus.
À titre d'exemple, l'ensemble d'événements pour les individus pourrait être du type {de couleur
acceptable, de couleur non acceptable}.
En général, la notation applicable à un processus stochastique discontinu est {X }, où X est le résultat de
i i
l'élément i dans le processus. Dans le cas où la caractéristique est une propriété X , il s'agit d'une valeur
i
attribuée à chacun des événements de l'ensemble des événements qui sert à caractériser le processus.
Pour un processus discontinu, l'indice i est normalement le numéro de l'individu dans la séquence
d'individus générée. Cependant, il peut parfois se révéler plus approprié d'utiliser comme indice le temps
par rapport à un point fixe.
⎯ Lorsque le processus est continu, il existe un grand nombre de possibilités pour l'indice, selon la nature
du produit. Lorsque le produit est, par exemple, une bobine de papier, l'indice pourrait être la longueur
effective par rapport à un point de départ ou il pourrait être le temps par rapport à un point fixe.
Il convient de noter qu'un processus stochastique comporte normalement une corrélation propre.
Un processus stochastique est stationnaire ou non stationnaire. Le présent document ne donne pas une
définition rigoureuse d'un processus stochastique stationnaire. Toutefois, un processus stationnaire comporte
une répartition de X , qui est indépendante de i.
i
Pour obtenir un processus qui satisfait aux spécifications, il convient que le processus stochastique soit
stationnaire ou qu'il soit non stationnaire et bien défini (par exemple un processus périodique).
L'évaluation d'un processus requiert une étude de la performance. Il convient en fait qu'une étude de la
performance débute comme une étude théorique de tous les éléments contenus dans le processus avant la
mise en œuvre physique dudit processus. Lorsque les paramètres des différentes phases du processus ont
été analysés et redéfinis, le processus est mis en œuvre (peut-être uniquement comme un processus d'essai).
L'échantillonnage du processus mis en œuvre constitue la base d'initiation de la partie numérique de l'étude
de la performance. Il convient de répondre correctement à un certain nombre de questions concernant le
processus, et ce, au-delà de tout doute raisonnable. La question la plus importante à laquelle il doit être
répondu consiste à déterminer si le processus est un processus stationnaire stable ou prévisible pendant une
période raisonnable. Il est alors important, pour le processus, d'identifier sa loi de probabilité et d'obtenir des
estimations des paramètres de répartition avec une variance faible raisonnable. Sur la base de ces
informations, la phase suivante de l'étude de la performance consisterait à représenter les propriétés des
caractéristiques examinées et à déterminer si elles sont acceptables. Si les propriétés ne peuvent pas être
acceptées, les paramètres du processus proprement dit doivent être modifiés de manière à obtenir un
processus ayant des propriétés acceptables.
Considérons, dans un premier temps, un processus bien défini et mis en œuvre qui a été accepté au moyen
d'une étude de la performance. La phase suivante du processus consisterait alors à s'assurer que les
paramètres du processus et, ainsi, du processus stochastique, ne changent pas, ou changent de manière
prévisible. Pour ce faire, il y a lieu de définir une étude d'aptitude appropriée.
Les études portant sur les indices de performance et d'aptitude sont de plus en plus utilisées pour évaluer le
matériel de production, un processus, voire un équipement de mesure, par rapport aux critères de
spécification. Différents types d'études sont utilisés selon les circonstances.
0.2 Les concepts d'aptitude et de performance ont fait l'objet de profonds changements d'opinion. Le
changement le plu
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