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1、BRITISH STANDARD BS ISO 5725-4:1994 Implementation of ISO 5725-4:1994 Accuracy (trueness and precision) of measurement methods and results Part 4: Basic methods for the determination of the trueness of a standard measurement method BS ISO 5725-4:1994 This British Standard, having been prepared under
2、 the direction of the Management Systems Sector Board, was published under the authority of the Standards Board and comes into effect on 15 April 1995 BSI 11-1999 The following BSI references relate to the work on this standard: Committee reference QMS/16 Draft for comment 90/97780 DC ISBN 0 580 240
3、28 2 Committees responsible for this British Standard The preparation of this British Standard was entrusted to Technical Committee QMS/16, Precision of test methods, upon which the following bodies were represented: British Gas plc Chemical Industries Association Consumers Association Department of
4、 Trade and Industry (Laboratory of the Government Chemist) Department of Trade and Industry (National Physical Laboratory) Institute of Quality Assurance Ministry of Agriculture, Fisheries and Food Ministry of Defence Royal Society of Chemistry University of London Amendments issued since publicatio
5、n Amd. No.DateComments BS ISO 5725-4:1994 BSI 11-1999i Contents Page Committees responsibleInside front cover National forewordii Forewordiv Text of ISO 5725-41 BS ISO 5725-4:1994 ii BSI 11-1999 National foreword This British Standard reproduces verbatim ISO 5725-4:1994 and implements it as the UK n
6、ational standard. Parts 1 to 6 of BS ISO 5725 together supersede BS 5497-1:1987 which will be withdrawn upon the publication of BS ISO 5725-5. This British Standard is published under the direction of the Management Systems Sector Board whose Technical Committee QMS/16 has the responsibility to: aid
7、 enquirers to understand the text; present to the responsible international committee any enquiries on interpretation, or proposals for change, and keep UK interests informed; monitor related international and European developments and promulgate them in the UK. NOTEInternational and European Standa
8、rds, as well as overseas standards, are available from Customer Services, BSI, 389 Chiswick High Road, London W4 4AL. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a
9、 British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, the ISO title page, pages ii to iv, pages 1 to 22, an inside back cover and a back cover. This standard has been updated (see co
10、pyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. ISO 5725-4:1994(E) ii BSI 11-1999 Contents Page Forewordiv Introduction1 1Scope1 2Normative references2 3Definitions2 4Determination of the bias of a standard measurement
11、method by an interlaboratory experiment2 4.1The statistical model2 4.2Reference material requirements2 4.3Experimental design considerations when estimating the bias of a measurement method3 4.4Cross-references to ISO 5725-1 and ISO 5725-23 4.5Required number of laboratories3 4.6Statistical evaluati
12、on3 4.7Interpretation of the results of the statistical evaluation3 5Determination of the laboratory bias of one laboratory using a standard measurement method5 5.1Carrying out the experiment5 5.2Cross-references to ISO 5725-1 and ISO 5725-26 5.3Number of test results6 5.4Choice of reference materia
13、ls6 5.5Statistical analysis6 6The report to, and the decisions to be taken by, the panel7 6.1Report by the statistical expert7 6.2Decisions by the panel7 7Utilization of trueness data7 Annex A (normative) Symbols and abbreviations used in ISO 57258 Annex B (informative) Example of an accuracy experi
14、ment10 B.1Description of the experiment10 B.2Precision assessment10 B.3Trueness assessment11 B.4Further analysis11 Annex C (informative) Derivation of equations20 C.1Equations (5) and (6) (see 4.5)20 C.2Equations (19) and (20) (see 5.3)22 Annex D (informative) BibliographyInside back cover Figure B.
15、1 Manganese content in iron ores: Test results at level 114 Figure B.2 Manganese content in iron ores: Test results at level 215 Figure B.3 Manganese content in iron ores: Test results at level 316 Figure B.4 Manganese content in iron ores: Test results at level 417 Figure B.5 Manganese content in i
16、ron ores: Test results at level 518 Figure B.6 Manganese content in iron ores: h values grouped by laboratories19 Figure B.7 Manganese content in iron ores: k values grouped by laboratories19 Figure B.8 Manganese content in iron ores: Repeatability and reproducibility standard deviations as linear f
17、unctions of the concentration level m20 ISO 5725-4:1994(E) BSI 11-1999iii Page Table 1 Values showing the uncertainty in the estimate of the bias of the measurement method4 Table B.1 Manganese content in iron ores: Accepted reference values11 Table B.2 Manganese content in iron ores: Analytical resu
18、lts as percentage Mn11 Table B.3 Manganese content in iron ores: Laboratory means and laboratory variances12 Table B.4 Manganese content in iron ores: Outliers and stragglers13 Table B.5 Manganese content in iron ores: Estimation of repeatability and reproducibility standard deviations and bias of t
19、he measurement method13 ISO 5725-4:1994(E) iv BSI 11-1999 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 committe
20、es. 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 Inte
21、rnational Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. 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
22、bodies casting a vote. International Standard ISO 5725-4 was prepared by Technical Committee ISO/TC 69, Applications of statistical methods, Subcommittee SC 6, Measurement methods and results. ISO 5725 consists of the following parts, under the general title Accuracy (trueness and precision) of meas
23、urement methods and results: Part 1: General principles and definitions; Part 2: Basic method for the determination of repeatability and reproducibility of a standard measurement method; Part 3: Intermediate measures of the precision of a standard measurement method; Part 4: Basic methods for the de
24、termination of the trueness of a standard measurement method; Part 5: Alternative methods for the determination of the precision of a standard measurement method; Part 6: Use in practice of accuracy values. Parts 1 to 6 of ISO 5725 together cancel and replace ISO 5725:1986, which has been extended t
25、o cover trueness (in addition to precision) and intermediate precision conditions (in addition to repeatability and reproducibility conditions). Annex A forms an integral part of this part of ISO 5725. Annex B, Annex C and Annex D are for information only. ISO 5725-4:1994(E) BSI 11-19991 Introductio
26、n 0.1 ISO 5725 uses two terms “trueness” and “precision” to describe the accuracy of a measurement method. “Trueness” refers to the closeness of agreement between the arithmetic mean of a large number of test results and the true or accepted reference value. “Precision” refers to the closeness of ag
27、reement between test results. 0.2 General consideration of these quantities is given in ISO 5725-1 and so has not been repeated in this part of ISO 5725. ISO 5725-1 should be read in conjunction with all other parts of ISO 5725, including this part, because it gives the underlying definitions and ge
28、neral principles. 0.3 The “trueness” of a measurement method is of interest when it is possible to conceive of a true value for the property being measured. Although, for some measurement methods, the true value cannot be known exactly, it may be possible to have an accepted reference value for the
29、property being measured; for example, if suitable reference materials are available, or if the accepted reference value can be established by reference to another measurement method or by preparation of a known sample. The trueness of the measurement method can be investigated by comparing the accep
30、ted reference value with the level of the results given by the measurement method. Trueness is normally expressed in terms of bias. Bias can arise, for example, in chemical analysis if the measurement method fails to extract all of an element, or if the presence of one element interferes with the de
31、termination of another. 0.4 Two measures of trueness may be of interest and both are considered in this part of ISO 5725. a) Bias of the measurement method: where there is a possibility that the measurement method may give rise to a bias, which persists wherever and whenever the measurement is done,
32、 then it is of interest to investigate the “bias of the measurement method” (as defined in ISO 5725-1). This requires an experiment involving many laboratories, very much as described in ISO 5725-2. b) Laboratory bias: measurements within a single laboratory can reveal the “laboratory bias” (as defi
33、ned in ISO 5725-1). If it is proposed to undertake an experiment to estimate laboratory bias, then it should be realized that the estimate will be valid only at the time of the experiment. Further regular testing is required to show that the laboratory bias does not vary; the method described in ISO
34、 5725-6 may be used for this. 1 Scope 1.1 This part of ISO 5725 provides basic methods for estimating the bias of a measurement method and the laboratory bias when a measurement method is applied. 1.2 It is concerned exclusively with measurement methods which yield measurements on a continuous scale
35、 and give a single value as the test result, although the single value may be the outcome of a calculation from a set of observations. 1.3 In order that the measurements are made in the same way, it is important that the measurement method has been standardized. All measurements are to be carried ou
36、t according to that standard method. 1.4 Bias values give quantitative estimates of the ability of a measurement method to give the correct (true) result. When a value for the bias of a measurement method is quoted, together with a test result obtained by that method, there is an implication that th
37、e same characteristic is being measured in exactly the same way. 1.5 This part of ISO 5725 can be applied only if the accepted reference value can be established as a conventional true value, for example by measurement standards or suitable reference materials or by referring to a reference measurem
38、ent method or by preparation of a known sample. Reference materials could be either a) certified reference materials; b) materials manufactured for the purpose of the experiment with known properties; or c) materials whose properties have been established by measurements using an alternative measure
39、ment method whose bias is known to be negligible. 1.6 This part of ISO 5725 considers only those cases where it is sufficient to estimate bias on one level at a time. It is not applicable if the bias in the measurement of one property is affected by the level of a second property (i.e. it does not c
40、onsider interferences). Comparison of the trueness of two measurement methods is considered in ISO 5725-6. NOTE 1In this part of ISO 5725, bias is considered only at one level at a time. Therefore the index j for the level has been omitted throughout. ISO 5725-4:1994(E) 2 BSI 11-1999 2 Normative ref
41、erences The following standards contain provisions which, through reference in this text, constitute provisions of this part of ISO 5725. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this part of ISO 5725 are
42、 encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. Members of IEC and ISO maintain registers of currently valid International Standards. ISO 3534-1:1993, Statistics Vocabulary and symbols Part 1: Probability and general statistical terms
43、. ISO 5725-1:1994, Accuracy (trueness and precision) of measurement methods and results Part 1: General principles and definitions. ISO 5725-2:1994, Accuracy (trueness and precision) of measurement methods and results Part 2: Basic method for the determination of repeatability and reproducibility of
44、 a standard measurement method. 3 Definitions For the purposes of this part ISO 5725, the definitions given in ISO 3534-1 and in ISO 5725-1 apply. The symbols used in ISO 5725 are given in Annex A. 4 Determination of the bias of a standard measurement method by an interlaboratory experiment 4.1 The
45、statistical model In the basic model described in subclause 5.1 of ISO 5725-1:1994, the general mean m may be replaced by where The model becomes Equation (2) is used when is of interest. Here B is the laboratory component of bias, i.e. the component in a test result representing the between-laborat
46、ory variation. The laboratory bias, , is given by so the model may be written Equation (4) is used when is of interest. 4.2 Reference material requirements If reference materials are used, the requirements given in 4.2.1 and 4.2.2 shall be satisfied. Reference materials shall be homogeneous. 4.2.1 C
47、hoice of reference materials 4.2.1.1 The reference material shall have known properties at the level appropriate to the level at which the standard measurement method is intended to be applied, e.g. concentration. In some cases it will be important to include, in the assessment experiment, a series
48、of reference materials, each corresponding to a different level of the property, as the bias of the standard measurement method may be different at different levels. The reference material should have a matrix as close as possible to the matrix of the material to be subjected to the standard measure
49、ment method, e.g. carbon in coal or carbon in steel. 4.2.1.2 The quantity of the reference material shall be sufficient for the entire experimental programme, including some in reserve if this is considered necessary. 4.2.1.3 Wherever possible, the reference material should have stable properties throughout the experiment. There are three cases, as follows. a) The properties are stable: no precautions are necessary. b) The certified value of the property may be influenced by storage conditions: the container should b
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