ISO INTERNATIONAL STANDARD 21748 Secondedition 2017-04 Guidance for the use of repeatability, reproducibility and trueness estimates in measurement uncertainty evaluation Lignes directrices relatives a I'utilisation d'estimations de la répétabilité, de la reproductibilité et de la justesse dans I'évaluation de I'incertitude de mesure Reference number IS0 21748:2017(E) International Organization for Standardization @ IS0 2017 ZHEJIANG INST OF STANDARDIZATION C15956617 Not for Resale, 2017/8/21 02:38:54 ted without license from IHS IS0 21748:2017(E) COPYRIGHTPROTECTEDDOCUMENT IS02017,PublishedinSwitzerland All rights reserved. Unless otherwise specified, no part of this publication may 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 ISO's member body in the country of the requester. ISO copyright office Ch. de Blandonnet 8 . CP 401 CH-1214 Vernier, Geneva, Switzerland Tel. +41 22 749 01 11 Fax+412274909 47 [email protected] www.iso.org Intenationai br PrganizationforStandardization icensee-ZHEJIANG INST OF STANDARDIZRoISQ s1.7 - All rights reserved Not for Resale, 2017/8/21 02:38:54 etworking permitted without license from IHS IS0 21748:2017(E) Contents Page Foreword ..V Introduction. ..vii 1 Scope. 2 Normative references 3 Terms and definitions 4 Symbols. ..5 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. ..8 5.4 Repeatability data .9 6 Evaluating uncertainty using repeatability, reproducibility and trueness estimates .9 6.1 Procedure for evaluating measurement uncertainty .9 6.2 Differences between expected and actual precision .10 7 Establishing the relevance of method performance data to measurement results from a particular measurement process ..10 7.1 General .10 7.2 Demonstrating control of the laboratory component of bias .10 7.2.1 Generalreguirements .10 7.2.2 Methods of demonstrating control of thelaboratory component ofbias ..10 7.2.3 Detection of significant laboratory component of bias .13 7.3 Verification of repeatability .13 7.4 Continued verification of performance. .13 8 Establishing relevance to the test item .13 8.1 General .13 8.2 Sampling .14 8.2.1 Inclusion of sampling process. ..14 8.2.2 Inhomogeneity .14 8.3 Sample preparation and pre-treatment .14 8.4 Changes in test-item type .14 8.5 Variation of uncertainty with level of response ..14 8.5.1 Adjusting SR 14 8.5.2 Changes in other contributions to uncertainty ..15 9 Additional factors ..15 10 General expression for combined standard uncertainty ..16 11 Uncertainty budgets based on collaborative study data ..16 12 Evaluation of uncertainty for a combined result ..18 13 Expression of uncertainty information ..18 13.1 General expression. ..18 13.2 Choice of coverage factor .18 13.2.1 General. .18 13.2.2 Level of confidence desired .18 13.2.3 Degrees of freedom associated with the estimate ..18 14 Comparison of method performance figures and uncertainty data .19 14.1 Basic assumptions for comparison .19 14.2 Comparison procedure. ..19 14.3 Reasons for differences .20 Annex A (informative) Approaches to uncertainty evaluation ..21 iii ISee=ZHEJIANG INST OF STANDARDIZATION C1 5956617 thout license from IHS Not for Resale, 2017/8/21 02:38:54