1、Guidance for the use of repeatability, reproducibility and trueness estimates in measurement uncertainty evaluationBS ISO 21748:2017BSI Standards PublicationWB11885_BSI_StandardCovs_2013_AW.indd 1 15/05/2013 15:06 ISO 2017Guidance for the use of repeatability, reproducibility and trueness estimates
2、in measurement uncertainty evaluationLignes directrices relatives lutilisation destimations de la rptabilit, de la reproductibilit et de la justesse dans lvaluation de lincertitude de mesureINTERNATIONALSTANDARDISO21748Second edition2017-04Reference numberISO 21748:2017(E)National forewordThis Briti
3、sh Standard is the UK implementation of ISO 21748:2017. It supersedes BS ISO 21748:2010, which is withdrawn.The UK participation in its preparation was entrusted to Technical Committee SS/6, Precision of test methods.A list of organizations represented on this committee can be obtained on request to
4、 its secretary.This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application. The British Standards Institution 2017 Published by BSI Standards Limited 2017ISBN 978 0 580 94905 0ICS 17.020Compliance with a British Standard
5、cannot confer immunity from legal obligations.This British Standard was published under the authority of the Standards Policy and Strategy Committee on 31 July 2017.Amendments/corrigenda issued since publicationDate Text affectedBRITISH STANDARDBS ISO 21748:2017 ISO 2017Guidance for the use of repea
6、tability, reproducibility and trueness estimates in measurement uncertainty evaluationLignes directrices relatives lutilisation destimations de la rptabilit, de la reproductibilit et de la justesse dans lvaluation de lincertitude de mesureINTERNATIONAL STANDARDISO21748Second edition2017-04Reference
7、numberISO 21748:2017(E)BS ISO 21748:2017ISO 21748:2017(E)ii ISO 2017 All rights reservedCOPYRIGHT PROTECTED DOCUMENT ISO 2017, Published in SwitzerlandAll rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form or by any means, ele
8、ctronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below or ISOs member body in the country of the requester.ISO copyright officeCh. de Blandonnet 8 CP 401CH-1214 Verni
9、er, Geneva, SwitzerlandTel. +41 22 749 01 11Fax +41 22 749 09 47copyrightiso.orgwww.iso.orgBS ISO 21748:2017ISO 21748:2017(E)ii ISO 2017 All rights reservedCOPYRIGHT PROTECTED DOCUMENT ISO 2017, Published in SwitzerlandAll rights reserved. Unless otherwise specified, no part of this publication may
10、be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below or ISOs member body in the country of the r
11、equester.ISO copyright officeCh. de Blandonnet 8 CP 401CH-1214 Vernier, Geneva, SwitzerlandTel. +41 22 749 01 11Fax +41 22 749 09 47copyrightiso.orgwww.iso.orgISO 21748:2017(E)Foreword vIntroduction vii1 Scope . 12 Normative references 13 Terms and definitions . 14 Symbols 55 Principles . 75.1 Indiv
12、idual results and measurement process performance 75.2 Applicability of reproducibility data 75.3 Basic equations for the statistical model 85.4 Repeatability data 96 Evaluating uncertainty using repeatability, reproducibility and trueness estimates . 96.1 Procedure for evaluating measurement uncert
13、ainty . 96.2 Differences between expected and actual precision .107 Establishing the relevance of method performance data to measurement results from a particular measurement process 107.1 General 107.2 Demonstrating control of the laboratory component of bias 107.2.1 General requirements .107.2.2 M
14、ethods of demonstrating control of the laboratory component of bias .107.2.3 Detection of significant laboratory component of bias .137.3 Verification of repeatability 137.4 Continued verification of performance . 138 Establishing relevance to the test item 138.1 General 138.2 Sampling 148.2.1 Inclu
15、sion of sampling process . 148.2.2 Inhomogeneity 148.3 Sample preparation and pre-treatment . 148.4 Changes in test-item type . 148.5 Variation of uncertainty with level of response 148.5.1 Adjusting sR148.5.2 Changes in other contributions to uncertainty 159 Additional factors .1510 General express
16、ion for combined standard uncertainty 1611 Uncertainty budgets based on collaborative study data 1612 Evaluation of uncertainty for a combined result .1813 Expression of uncertainty information .1813.1 General expression . 1813.2 Choice of coverage factor 1813.2.1 General. 1813.2.2 Level of confiden
17、ce desired . 1813.2.3 Degrees of freedom associated with the estimate .1814 Comparison of method performance figures and uncertainty data 1914.1 Basic assumptions for comparison. 1914.2 Comparison procedure . 1914.3 Reasons for differences . 20Annex A (informative) Approaches to uncertainty evaluati
18、on .21 ISO 2017 All rights reserved iiiContents PageBS ISO 21748:2017ISO 21748:2017(E)Annex B (informative) Experimental uncertainty evaluation .26Annex C (informative) Examples of uncertainty calculations .27Bibliography .37iv ISO 2017 All rights reservedBS ISO 21748:2017ISO 21748:2017(E)Annex B (i
19、nformative) Experimental uncertainty evaluation .26Annex C (informative) Examples of uncertainty calculations .27Bibliography .37iv ISO 2017 All rights reserved ISO 21748:2017(E)ForewordISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (I
20、SO 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, gov
21、ernmental 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.The procedures used to develop this document and those intended for its further mainte
22、nance 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).Att
23、ention 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 Introducti
24、on 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 constitute an endorsement.For an explanation on the voluntary nature of standards, the meaning of ISO specific te
25、rms and expressions related to conformity assessment, as well as information about ISOs 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/
26、TC 69, Applications of statistical methods, Subcommittee SC 6, Measurement methods and results.This second edition cancels and replaces the first edition (ISO 21748:2010), of which it constitutes a minor revision.The changes compared to the previous edition are as follows: minor change in the title
27、(estimation to evaluation) to reflect preferred use of terms (see third list item); minor changes in wording and format to conform to current ISO Directives, which included the addition of Clause 2 and renumbering of subsequent clauses; the phrases “estimation of measurement uncertainty” (and simila
28、r usage of “estimate”) and “evaluation of measurement uncertainty” (and similar usage of “evaluate”) have been amended to distinguish quantitative estimates of the components of uncertainty from the process of evaluations of measurement uncertainty, which can include additional relevant consideratio
29、ns; the word “standard” has been added before “uncertainty” where appropriate, for clarity; redundant definitions of terms defined as squared quantities, where the standard deviation was also defined s2b, s2inh, s2L, s2r, s2W, u2(y), 2L, 2r have been removed; in the definition of rij, “in the interv
30、al -1 to +1” was removed; in the definition of the term sinh, “uncertainty” was changed to “standard deviation”; in the definitions for u( y), ui( y) and u(Y), U( y), equations were removed (not necessary for standard terms); the symbols from all definitions of terms where they had been included (co
31、mbined standard uncertainty, coverage factor, expanded uncertainty, standard uncertainty) have been removed; ISO 2017 All rights reserved vBS ISO 21748:2017ISO 21748:2017(E) the definition of y0has been removed because the term is not used in the document; in 7.4, first dash, “quality control charts
32、” has been replaced with “control charts”; a note has been added to Clause 10 (previously Clause 9); in 13.1, 14.1 and 14.3 (previously 12.1, 13.1 and 13.3), “combined” has been added before “standard uncertainty”; in 13.2.1 and 13.2.2 (previously 12.2.1 and 12.2.2), the word “combined” has been rem
33、oved before “expanded uncertainty”; in A.1, changed italics “standard uncertainties” to standard text; in A.1, 7th paragraph (3rd from end), “combined standard uncertainties u(xi)” has been changed to “additional standard uncertainties u(y)”; in C.3, title, “Uncertainty for AOAC method 990.12” has b
34、een replaced with “Uncertainty for measurements obtained by AOAC method 990.12”; in C.3.2, “eight laboratories” has been replaced with “twelve laboratories “; in C.4.4, “0,07 g/kg (0,7 % as mass fraction)” has been changed to “7 g/kg (0,7 % as mass fraction)”; References 27 and 28 have been updated.
35、vi ISO 2017 All rights reservedBS ISO 21748:2017ISO 21748:2017(E) the definition of y0has been removed because the term is not used in the document; in 7.4, first dash, “quality control charts” has been replaced with “control charts”; a note has been added to Clause 10 (previously Clause 9); in 13.1
36、, 14.1 and 14.3 (previously 12.1, 13.1 and 13.3), “combined” has been added before “standard uncertainty”; in 13.2.1 and 13.2.2 (previously 12.2.1 and 12.2.2), the word “combined” has been removed before “expanded uncertainty”; in A.1, changed italics “standard uncertainties” to standard text; in A.
37、1, 7th paragraph (3rd from end), “combined standard uncertainties u(xi)” has been changed to “additional standard uncertainties u(y)”; in C.3, title, “Uncertainty for AOAC method 990.12” has been replaced with “Uncertainty for measurements obtained by AOAC method 990.12”; in C.3.2, “eight laboratori
38、es” has been replaced with “twelve laboratories “; in C.4.4, “0,07 g/kg (0,7 % as mass fraction)” has been changed to “7 g/kg (0,7 % as mass fraction)”; References 27 and 28 have been updated.vi ISO 2017 All rights reserved ISO 21748:2017(E)IntroductionKnowledge of the uncertainty associated with me
39、asurement results is essential to the interpretation of the results. Without quantitative evaluations 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 bas
40、ed on limits have been broken. Without information on uncertainty, there is a risk of misinterpretation of results. Incorrect decisions taken on such a basis can result in unnecessary expenditure in industry, incorrect prosecution in law, or adverse health or social consequences.Laboratories operati
41、ng under ISO/IEC 17025 accreditation and related systems are accordingly required to evaluate measurement uncertainty for measurement and test results and report the uncertainty where relevant. ISO/IEC Guide 98-3 is a widely adopted standard approach. However, it applies to situations where a model
42、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. This document provides an appropriate and economic methodology for estimating uncertainty associated with the results of these methods, whi
43、ch complies fully with the relevant principles of the GUM, while taking account of method performance data obtained by collaborative study.The general approach used in this document requires the following. Estimates of the repeatability, reproducibility and trueness of the method in use, obtained by
44、 collaborative study as described in ISO 5725-2, be available from published information about the test method in use. These provide estimates of the intra-laboratory and inter-laboratory components of variance, together with an estimate of uncertainty associated with the trueness of the method. The
45、 laboratory confirms 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
46、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. This esti
47、mate can serve, with other contributions, in the evaluation of uncertainty, or in some cases can be the final, stated, uncertainty.The general principle of using reproducibility data in uncertainty evaluation is sometimes called a “top-down” approach.The dispersion of results obtained in a collabora
48、tive study is often also usefully compared with measurement uncertainty evaluated 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. ISO 2017 All
49、rights reserved viiBS ISO 21748:2017BS ISO 21748:2017Guidance for the use of repeatability, reproducibility and trueness estimates in measurement uncertainty evaluation1 ScopeThis document gives guidance for evaluation of measurement uncertainties using data obtained from studies conducted in accordance with ISO 5725-2, and comparison of collaborative study results with measurement uncertainty (MU) obtained using formal principles of uncertainty propagation (see Clause 14)
