SIST-TS ISO/TS 21748:2006
(Main)Guidance for the use of repeatability, reproducibility and trueness estimates in measurement uncertainty estimation
Guidance for the use of repeatability, reproducibility and trueness estimates in measurement uncertainty estimation
TS 21748:2004 gives guidance for the evaluation of measurement uncertainties using data obtained from studies conducted in accordance with ISO 5725-2, and for the comparison of collaborative study results with measurement uncertainty obtained using formal principles of uncertainty propagation. TS 21748:2003 is applicable in all measurement and test fields where an uncertainty associated with a result has to be determined, but does not describe the application of repeatability data in the absence of reproducibility data. The recommendations in this document are primarily for guidance.
Lignes directrices relatives à l'utilisation d'estimations de la répétabilité, de la reproductibilité et de la justesse dans l'évaluation de l'incertitude de mesure
L'ISO/TS 21748:2004 donne des lignes directrices en vue, d'une part, d'évaluer l'incertitude de mesure à partir de données obtenues lors d'études menées conformément à l'ISO 5725-2 et, d'autre part, de comparer les résultats d'une étude collaborative à l'incertitude de mesure obtenue en appliquant des principes formels de propagation de l'incertitude. L'ISO/TS 21748:2004 est applicable dans tous les domaines de mesure et d'essai nécessitant la détermination d'une incertitude associée à un résultat, mais ne décrit pas l'utilisation de données de répétabilité en l'absence de données de reproductibilité. Les recommandations de ce document sont avant tout indicatives.
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TECHNICAL ISO/TS
SPECIFICATION 21748
First edition
2004-03-15
Guidance for the use of repeatability,
reproducibility and trueness estimates in
measurement uncertainty estimation
Lignes directrices relatives à l'utilisation d'estimations de la répétabilité,
de la reproductibilité et de la justesse dans l'évaluation de l'incertitude
de mesure
Reference number
©
ISO 2004
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 2004
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 2004 – All rights reserved
Contents Page
Foreword. iv
Introduction . v
1 Scope. 1
2 Normative references . 1
3 Terms and definitions. 2
4 Symbols . 4
5 Principles . 7
5.1 Individual results and measurement process performance. 7
5.2 Applicability of reproducibility data. 7
5.3 Basic equations for the statistical model. 7
5.4 Repeatability data . 8
6 Evaluating uncertainty using repeatability, reproducibility and trueness estimates . 8
6.1 Procedure for evaluating measurement uncertainty. 8
6.2 Differences between expected and actual precision . 9
7 Establishing the relevance of method performance data to measurement results from a
particular measurement process . 9
7.1 General. 9
7.2 Demonstrating control of the laboratory component of bias. 9
7.3 Verification of repeatability. 11
7.4 Continued verification of performance. 12
8 Establishing relevance to the test item . 12
8.1 General. 12
8.2 Sampling . 12
8.3 Sample preparation and pre-treatment. 13
8.4 Changes in test-item type . 13
8.5 Variation of uncertainty with level of response . 13
9 Additional factors. 14
10 General expression for combined standard uncertainty. 14
11 Uncertainty budgets based on collaborative study data. 15
12 Evaluation of uncertainty for a combined result . 16
13 Expression of uncertainty information . 17
13.1 General expression. 17
13.2 Choice of coverage factor. 17
14 Comparison of method performance figures and uncertainty data . 17
14.1 Basic assumptions for comparison . 17
14.2 Comparison procedure. 18
14.3 Reasons for differences . 18
Annex A (informative) Approaches to uncertainty estimation. 19
Annex B (informative) Experimental uncertainty evaluation . 24
Annex C (informative) Examples of uncertainty calculations. 25
Bibliography . 29
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 other circumstances, particularly when there is an urgent market requirement for such documents, a
technical committee may decide to publish other types of normative document:
an ISO Publicly Available Specification (ISO/PAS) represents an agreement between technical experts in
an ISO working group and is accepted for publication if it is approved by more than 50 % of the members
of the parent committee casting a vote;
an ISO Technical Specification (ISO/TS) represents an agreement between the members of a technical
committee and is accepted for publication if it is approved by 2/3 of the members of the committee casting
a vote.
An ISO/PAS or ISO/TS is reviewed after three years in order to decide whether it will be confirmed for a
further three years, revised to become an International Standard, or withdrawn. If the ISO/PAS or ISO/TS is
confirmed, it is reviewed again after a further three years, at which time it must either be transformed into an
International Standard or be withdrawn.
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/TS 21748 was prepared by Technical Committee ISO/TC 69, Applications of statistical methods,
Subcommittee SC 6, Measurement methods and results.
iv © ISO 2004 – All rights reserved
Introduction
Knowledge of the uncertainty associated with measurement results is essential to the interpretation of the
results. Without quantitative assessments of uncertainty, it is impossible to decide whether observed
differences between results reflect more than experimental variability, whether test items comply with
specifications, or whether laws based on limits have been broken. Without information on uncertainty, there is
a risk of misinterpretation of results. Incorrect decisions taken on such a basis may result in unnecessary
expenditure in industry, incorrect prosecution in law, or adverse health or social consequences.
Laboratories operating under ISO 17025 accreditation and related systems are accordingly required to
evaluate measurement uncertainty for measurement and test results and report the uncertainty where relevant.
The Guide to the expression of uncertainty in measurement (GUM), published by ISO, is a widely adopted
standard approach. However, it applies to situations where a model of the measurement process is available.
A very wide range of standard test methods is, however, subjected to collaborative study in accordance with
ISO 5725-2:1994. This Technical Specification provides an appropriate and economic methodology for
estimating uncertainty associated with the results of these methods, which complies fully with the relevant
principles of the GUM, whilst taking account of method performance data obtained by collaborative study.
The general approach used in this Technical Specification requires that
estimates of the repeatability, reproducibility and trueness of the method in use, obtained by collaborative
study as described in ISO 5725-2:1994, be available from published information about the test method in
use. These provide estimates of the intra- and inter-laboratory components of variance, together with an
estimate of uncertainty associated with the trueness of the method;
the laboratory confirm that its implementation of the test method is consistent with the established
performance of the test method by checking its own bias and precision. This confirms that the published
data are applicable to the results obtained by the laboratory;
any influences on the measurement results that were not adequately covered by the collaborative study
be identified and the variance associated with the results that could arise from these effects be quantified.
An uncertainty estimate is made by combining the relevant variance estimates in the manner prescribed by
the GUM.
The dispersion of results obtained in a collaborative study is often also usefully compared with measurement
uncertainty estimates obtained using GUM procedures as a test of full understanding of the method. Such
comparisons will be more effective given a consistent methodology for estimating the same parameter using
collaborative study data.
TECHNICAL SPECIFICATION ISO/TS 21748:2004(E)
Guidance for the use of repeatability, reproducibility and
trueness estimates in measurement uncertainty estimation
1 Scope
The Technical Specification gives guidance for
evaluation of measurement uncertainties using data obtained from studies conducted in accordance with
ISO 5725-2:1994;
comparison of collaborative study results with measurement uncertainty (MU) obtained using formal
principles of uncertainty propagation (see Clause 14).
ISO 5725-3:1994 provides additional models for studies of intermediate precision. However, while the same
general approach may be applied to the use of such extended models, uncertainty evaluation using these
models is not incorporated in the present Technical Specification.
This Technical Specification is applicable in all measurement and test fields where an uncertainty associated
with a result has to be determined.
This Technical Specification does not describe the application of repeatability data in the absence of
reproducibility data.
This Technical Specification assumes that recognized, non-negligible systematic effects are corrected, either
by applying a numerical correction as part of the method of measurement, or by investigation and removal of
the cause of the effect.
The recommendations in this Technical Specification are primarily for guidance. It is recognized that while the
recommendations p
...
TECHNICAL ISO/TS
SPECIFICATION 21748
First edition
2004-03-15
Guidance for the use of repeatability,
reproducibility and trueness estimates in
measurement uncertainty estimation
Lignes directrices relatives à l'utilisation d'estimations de la répétabilité,
de la reproductibilité et de la justesse dans l'évaluation de l'incertitude
de mesure
Reference number
©
ISO 2004
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 2004
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 2004 – All rights reserved
Contents Page
Foreword. iv
Introduction . v
1 Scope. 1
2 Normative references . 1
3 Terms and definitions. 2
4 Symbols . 4
5 Principles . 7
5.1 Individual results and measurement process performance. 7
5.2 Applicability of reproducibility data. 7
5.3 Basic equations for the statistical model. 7
5.4 Repeatability data . 8
6 Evaluating uncertainty using repeatability, reproducibility and trueness estimates . 8
6.1 Procedure for evaluating measurement uncertainty. 8
6.2 Differences between expected and actual precision . 9
7 Establishing the relevance of method performance data to measurement results from a
particular measurement process . 9
7.1 General. 9
7.2 Demonstrating control of the laboratory component of bias. 9
7.3 Verification of repeatability. 11
7.4 Continued verification of performance. 12
8 Establishing relevance to the test item . 12
8.1 General. 12
8.2 Sampling . 12
8.3 Sample preparation and pre-treatment. 13
8.4 Changes in test-item type . 13
8.5 Variation of uncertainty with level of response . 13
9 Additional factors. 14
10 General expression for combined standard uncertainty. 14
11 Uncertainty budgets based on collaborative study data. 15
12 Evaluation of uncertainty for a combined result . 16
13 Expression of uncertainty information . 17
13.1 General expression. 17
13.2 Choice of coverage factor. 17
14 Comparison of method performance figures and uncertainty data . 17
14.1 Basic assumptions for comparison . 17
14.2 Comparison procedure. 18
14.3 Reasons for differences . 18
Annex A (informative) Approaches to uncertainty estimation. 19
Annex B (informative) Experimental uncertainty evaluation . 24
Annex C (informative) Examples of uncertainty calculations. 25
Bibliography . 29
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 other circumstances, particularly when there is an urgent market requirement for such documents, a
technical committee may decide to publish other types of normative document:
an ISO Publicly Available Specification (ISO/PAS) represents an agreement between technical experts in
an ISO working group and is accepted for publication if it is approved by more than 50 % of the members
of the parent committee casting a vote;
an ISO Technical Specification (ISO/TS) represents an agreement between the members of a technical
committee and is accepted for publication if it is approved by 2/3 of the members of the committee casting
a vote.
An ISO/PAS or ISO/TS is reviewed after three years in order to decide whether it will be confirmed for a
further three years, revised to become an International Standard, or withdrawn. If the ISO/PAS or ISO/TS is
confirmed, it is reviewed again after a further three years, at which time it must either be transformed into an
International Standard or be withdrawn.
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/TS 21748 was prepared by Technical Committee ISO/TC 69, Applications of statistical methods,
Subcommittee SC 6, Measurement methods and results.
iv © ISO 2004 – All rights reserved
Introduction
Knowledge of the uncertainty associated with measurement results is essential to the interpretation of the
results. Without quantitative assessments of uncertainty, it is impossible to decide whether observed
differences between results reflect more than experimental variability, whether test items comply with
specifications, or whether laws based on limits have been broken. Without information on uncertainty, there is
a risk of misinterpretation of results. Incorrect decisions taken on such a basis may result in unnecessary
expenditure in industry, incorrect prosecution in law, or adverse health or social consequences.
Laboratories operating under ISO 17025 accreditation and related systems are accordingly required to
evaluate measurement uncertainty for measurement and test results and report the uncertainty where relevant.
The Guide to the expression of uncertainty in measurement (GUM), published by ISO, is a widely adopted
standard approach. However, it applies to situations where a model of the measurement process is available.
A very wide range of standard test methods is, however, subjected to collaborative study in accordance with
ISO 5725-2:1994. This Technical Specification provides an appropriate and economic methodology for
estimating uncertainty associated with the results of these methods, which complies fully with the relevant
principles of the GUM, whilst taking account of method performance data obtained by collaborative study.
The general approach used in this Technical Specification requires that
estimates of the repeatability, reproducibility and trueness of the method in use, obtained by collaborative
study as described in ISO 5725-2:1994, be available from published information about the test method in
use. These provide estimates of the intra- and inter-laboratory components of variance, together with an
estimate of uncertainty associated with the trueness of the method;
the laboratory confirm that its implementation of the test method is consistent with the established
performance of the test method by checking its own bias and precision. This confirms that the published
data are applicable to the results obtained by the laboratory;
any influences on the measurement results that were not adequately covered by the collaborative study
be identified and the variance associated with the results that could arise from these effects be quantified.
An uncertainty estimate is made by combining the relevant variance estimates in the manner prescribed by
the GUM.
The dispersion of results obtained in a collaborative study is often also usefully compared with measurement
uncertainty estimates obtained using GUM procedures as a test of full understanding of the method. Such
comparisons will be more effective given a consistent methodology for estimating the same parameter using
collaborative study data.
TECHNICAL SPECIFICATION ISO/TS 21748:2004(E)
Guidance for the use of repeatability, reproducibility and
trueness estimates in measurement uncertainty estimation
1 Scope
The Technical Specification gives guidance for
evaluation of measurement uncertainties using data obtained from studies conducted in accordance with
ISO 5725-2:1994;
comparison of collaborative study results with measurement uncertainty (MU) obtained using formal
principles of uncertainty propagation (see Clause 14).
ISO 5725-3:1994 provides additional models for studies of intermediate precision. However, while the same
general approach may be applied to the use of such extended models, uncertainty evaluation using these
models is not incorporated in the present Technical Specification.
This Technical Specification is applicable in all measurement and test fields where an uncertainty associated
with a result has to be determined.
This Technical Specification does not describe the application of repeatability data in the absence of
reproducibility data.
This Technical Specification assumes that recognized, non-negligible systematic effects are corrected, either
by applying a numerical correction as part of the method of measurement, or by investigation and removal of
the cause of the effect.
The recommendations in this Technical Specification are primarily for guidance. It is recognized that while the
recomme
...
SLOVENSKI STANDARD
01-april-2006
Napotek za uporabo ocen ponovljivosti, obnovljivosti in pravilnosti pri
ocenjevanju merilne negotovosti
Guidance for the use of repeatability, reproducibility and trueness estimates in
measurement uncertainty estimation
Lignes directrices relatives à l'utilisation d'estimations de la répétabilité, de la
reproductibilité et de la justesse dans l'évaluation de l'incertitude de mesure
Ta slovenski standard je istoveten z: ISO/TS 21748:2004
ICS:
17.020 Meroslovje in merjenje na Metrology and measurement
splošno in general
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
TECHNICAL ISO/TS
SPECIFICATION 21748
First edition
2004-03-15
Guidance for the use of repeatability,
reproducibility and trueness estimates in
measurement uncertainty estimation
Lignes directrices relatives à l'utilisation d'estimations de la répétabilité,
de la reproductibilité et de la justesse dans l'évaluation de l'incertitude
de mesure
Reference number
©
ISO 2004
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 2004
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 2004 – All rights reserved
Contents Page
Foreword. iv
Introduction . v
1 Scope. 1
2 Normative references . 1
3 Terms and definitions. 2
4 Symbols . 4
5 Principles . 7
5.1 Individual results and measurement process performance. 7
5.2 Applicability of reproducibility data. 7
5.3 Basic equations for the statistical model. 7
5.4 Repeatability data . 8
6 Evaluating uncertainty using repeatability, reproducibility and trueness estimates . 8
6.1 Procedure for evaluating measurement uncertainty. 8
6.2 Differences between expected and actual precision . 9
7 Establishing the relevance of method performance data to measurement results from a
particular measurement process . 9
7.1 General. 9
7.2 Demonstrating control of the laboratory component of bias. 9
7.3 Verification of repeatability. 11
7.4 Continued verification of performance. 12
8 Establishing relevance to the test item . 12
8.1 General. 12
8.2 Sampling . 12
8.3 Sample preparation and pre-treatment. 13
8.4 Changes in test-item type . 13
8.5 Variation of uncertainty with level of response . 13
9 Additional factors. 14
10 General expression for combined standard uncertainty. 14
11 Uncertainty budgets based on collaborative study data. 15
12 Evaluation of uncertainty for a combined result . 16
13 Expression of uncertainty information . 17
13.1 General expression. 17
13.2 Choice of coverage factor. 17
14 Comparison of method performance figures and uncertainty data . 17
14.1 Basic assumptions for comparison . 17
14.2 Comparison procedure. 18
14.3 Reasons for differences . 18
Annex A (informative) Approaches to uncertainty estimation. 19
Annex B (informative) Experimental uncertainty evaluation . 24
Annex C (informative) Examples of uncertainty calculations. 25
Bibliography . 29
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 other circumstances, particularly when there is an urgent market requirement for such documents, a
technical committee may decide to publish other types of normative document:
an ISO Publicly Available Specification (ISO/PAS) represents an agreement between technical experts in
an ISO working group and is accepted for publication if it is approved by more than 50 % of the members
of the parent committee casting a vote;
an ISO Technical Specification (ISO/TS) represents an agreement between the members of a technical
committee and is accepted for publication if it is approved by 2/3 of the members of the committee casting
a vote.
An ISO/PAS or ISO/TS is reviewed after three years in order to decide whether it will be confirmed for a
further three years, revised to become an International Standard, or withdrawn. If the ISO/PAS or ISO/TS is
confirmed, it is reviewed again after a further three years, at which time it must either be transformed into an
International Standard or be withdrawn.
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/TS 21748 was prepared by Technical Committee ISO/TC 69, Applications of statistical methods,
Subcommittee SC 6, Measurement methods and results.
iv © ISO 2004 – All rights reserved
Introduction
Knowledge of the uncertainty associated with measurement results is essential to the interpretation of the
results. Without quantitative assessments of uncertainty, it is impossible to decide whether observed
differences between results reflect more than experimental variability, whether test items comply with
specifications, or whether laws based on limits have been broken. Without information on uncertainty, there is
a risk of misinterpretation of results. Incorrect decisions taken on such a basis may result in unnecessary
expenditure in industry, incorrect prosecution in law, or adverse health or social consequences.
Laboratories operating under ISO 17025 accreditation and related systems are accordingly required to
evaluate measurement uncertainty for measurement and test results and report the uncertainty where relevant.
The Guide to the expression of uncertainty in measurement (GUM), published by ISO, is a widely adopted
standard approach. However, it applies to situations where a model of the measurement process is available.
A very wide range of standard test methods is, however, subjected to collaborative study in accordance with
ISO 5725-2:1994. This Technical Specification provides an appropriate and economic methodology for
estimating uncertainty associated with the results of these methods, which complies fully with the relevant
principles of the GUM, whilst taking account of method performance data obtained by collaborative study.
The general approach used in this Technical Specification requires that
estimates of the repeatability, reproducibility and trueness of the method in use, obtained by collaborative
study as described in ISO 5725-2:1994, be available from published information about the test method in
use. These provide estimates of the intra- and inter-laboratory components of variance, together with an
estimate of uncertainty associated with the trueness of the method;
the laboratory confirm that its implementation of the test method is consistent with the established
performance of the test method by checking its own bias and precision. This confirms that the published
data are applicable to the results obtained by the laboratory;
any influences on the measurement results that were not adequately covered by the collaborative study
be identified and the variance associated with the results that could arise from these effects be quantified.
An uncertainty estimate is made by combining the relevant variance estimates in the manner prescribed by
the GUM.
The dispersion of results obtained in a collaborative study is often also usefully compared with measurement
uncertainty estimates obtained using GUM procedures as a test of full understanding of the method. Such
comparisons will be more effective given a consistent methodology for estimating the same parameter using
collaborative study data.
TECHNICAL SPECIFICATION ISO/TS 21748:2004(E)
Guidance for the use of repeatability, reproducibility and
trueness estimates in measurement uncertainty estimation
1 Scope
The Technical Specification gives guidance for
evaluation of measurement uncertainties using data obtained from studies conducted
...
SPÉCIFICATION ISO/TS
TECHNIQUE 21748
Première édition
2004-03-15
Lignes directrices relatives à l'utilisation
d'estimations de la répétabilité, de la
reproductibilité et de la justesse dans
l'évaluation de l'incertitude de mesure
Guidance for the use of repeatability, reproducibility and trueness
estimates in measurement uncertainty estimation
Numéro de référence
©
ISO 2004
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quelque forme que ce soit et par aucun procédé, électronique ou mécanique, y compris la photocopie et les microfilms, sans l'accord écrit
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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 2004 – Tous droits réservés
Sommaire Page
Avant-propos. iv
Introduction . v
1 Domaine d'application. 1
2 Références normatives. 1
3 Termes et définitions . 2
4 Symboles. 4
5 Principes. 7
5.1 Résultats individuels et performance du processus de mesure . 7
5.2 Utilisation des données de reproductibilité . 7
5.3 Équations fondamentales pour le modèle statistique . 7
5.4 Données de répétabilité. 8
6 Évaluation de l’incertitude de mesure à l’aide des estimations de la répétabilité, de la
reproductibilité et de la justesse . 9
6.1 Procédure pour l’évaluation de l’incertitude de mesure. 9
6.2 Différences entre fidélité attendue et fidélité réelle. 9
7 Établissement de la pertinence des données de performance de la méthode aux résultats
de mesure à partir d’un processus de mesure particulier. 9
7.1 Généralités. 9
7.2 Démonstration du contrôle du composant de biais du laboratoire. 9
7.3 Vérification de la répétabilité . 12
7.4 Vérification continue de la performance . 12
8 Établissement de la pertinence de l’individu d’essai. 13
8.1 Généralités. 13
8.2 Échantillonnage. 13
8.3 Préparation et traitement préalable des échantillons . 13
8.4 Changements du type d’individu d’essai . 13
8.5 Variation de l’incertitude avec le niveau de réponse . 14
9 Facteurs supplémentaires. 14
10 Expression générale pour l’estimation de l’incertitude-type composée . 15
11 Budgets d’incertitude fondés sur des données d’études collaboratives . 15
12 Évaluation de l’incertitude pour un résultat composé. 17
13 Expression des données d’incertitude . 17
13.1 Expression générale. 17
13.2 Choix du facteur d’élargissement . 17
14 Comparaison des valeurs de performance d’une méthode et des données d’incertitude . 18
14.1 Hypothèses de base . 18
14.2 Procédure d’essai. 18
14.3 Raisons des différences. 19
Annexe A (informative) Méthodes d’estimation de l’incertitude. 20
Annexe B (informative) Évaluation expérimentale de l'incertitude . 25
Annexe C (informative) Exemples de calcul de l’incertitude de mesure . 26
Bibliographie . 31
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.
Dans d'autres circonstances, en particulier lorsqu'il existe une demande urgente du marché, un comité
technique peut décider de publier d'autres types de documents normatifs:
une Spécification publiquement disponible ISO (ISO/PAS) représente un accord entre les experts dans
un groupe de travail ISO et est acceptée pour publication si elle est approuvée par plus de 50 % des
membres votants du comité dont relève le groupe de travail;
une Spécification technique ISO (ISO/TS) représente un accord entre les membres d'un comité technique
et est acceptée pour publication si elle est approuvée par 2/3 des membres votants du comité.
Une ISO/PAS ou ISO/TS fait l'objet d'un examen après trois ans afin de décider si elle est confirmée pour trois
nouvelles années, révisée pour devenir une Norme internationale, ou annulée. Lorsqu'une ISO/PAS ou
ISO/TS a été confirmée, elle fait l'objet d'un nouvel examen après trois ans qui décidera soit de sa
transformation en Norme internationale soit de son annulation.
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/TS 21748 a été élaborée par le comité technique ISO/TC 69, Application des méthodes statistiques,
sous-comité SC 6, Méthodes et résultats de mesure.
iv © ISO 2004 – Tous droits réservés
Introduction
Pour pouvoir interpréter des résultats, il est essentiel de connaître l’incertitude associée aux résultats des
mesures. Sans évaluation quantitative de l’incertitude, il est impossible de décider si les différences
observées entre des résultats sont supérieures à la variabilité expérimentale, si les individus d’essai sont
conformes aux spécifications ou si des lois basées sur des limites ont été enfreintes. Sans information sur
l’incertitude, il existe un risque de mal estimer les résultats. Des décisions incorrectes prises sur ces bases
peuvent entraîner des dépenses inutiles pour l’industrie, des poursuites judiciaires inappropriées ou bien des
conséquences néfastes sur la santé ou pour la société.
Par conséquent, les laboratoires accrédités selon l’ISO 17025 et les systèmes connexes sont tenus d’évaluer
l’incertitude de mesure pour leurs résultats d’essai et de mesure et, le cas échéant, de rapporter cette
incertitude. Le Guide pour l’expression de l’incertitude de mesure (GUM), publié par l’ISO, constitue une
méthode normalisée largement adoptée. Néanmoins, il s’applique à des situations où un modèle complet du
processus de mesure est disponible. Un très vaste ensemble de méthodes d’essai normalisées est toutefois
l'objet d'études collaboratives selon l’ISO 5725-2:1994. La présente Spécification technique fournit une
méthodologie appropriée et économique d’estimation de l’incertitude associée aux résultats de ces méthodes,
en totale conformité avec les principes correspondants du GUM, tout en tenant compte des données de
performances des méthodes, obtenues par une étude collaborative.
L’approche générale utilisée dans la présente Spécification technique nécessite que
les estimations de la répétabilité, de la reproductibilité et de la justesse de la méthode utilisée, obtenues
par des études collaboratives telles que décrites dans l’ISO 5725-2, soient disponibles dans les
informations publiées sur la méthode d’essai utilisée; ces études collaboratives fournissent des
estimations de la composante de variance intralaboratoire et interlaboratoires, accompagnées d’une
estimation de l’incertitude associée à la justesse de la méthode;
le laboratoire confirme que la mise en œuvre de la méthode d’essai est cohérente avec la performance
définie de la méthode d’essai, en vérifiant son propre biais et sa propre fidélité; cela confirme que les
données publiées sont applicables aux résultats obtenus par le laboratoire;
toutes les influences sur les résultats de mesure qui ne sont pas correctement couvertes pour l’étude
collaborative soient identifiées et la variance associée aux résultats qui peut découler de ces effets soit
quantifiée.
Une estimation de l’incertitude est effectuée en combinant les estimations pertinentes de la variance telles
que prescrites dans le GUM.
À titre d’essai de compréhension globale de la méthode, il peut aussi être utile de comparer la dispersion des
résultats, obtenue dans une étude collaborative, aux estimations de l’incertitude de mesure obtenues en
utilisant les procédures du GUM. Ces comparaisons seront plus efficaces s'il est donné une méthodologie
cohérente d’estimation du même paramètre à partir de données d’une étude collaborative.
SPÉCIFICATION TECHNIQUE ISO/TS 21748:2004(F)
Lignes directrices relatives à l'utilisation d'estimations de la
répétabilité, de la reproductibilité et de la justesse dans
l'évaluation de l'incertitude de mesure
1 Domaine d'application
La présente Spécification technique donne des lignes directrices en vue
d’évaluer l’incertitude de mesure à partir de données obtenues lors d’études menées conformément à
l’ISO 5725-2:1994, et
de comparer les résultats d’une étude collaborative à l’incertitude de mesure obtenue en appliquant des
principes formels de propagation de l’incertitude (voir Article 14).
L’ISO 5725-3:1994 fournit des modèles supplémentaires d’ét
...
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