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 methodBSISO5725-4:1994 This British Standard, having been prepared under th
2、e directionof the Management Systems Sector Board, was published under the authorityofthe Standards Boardand 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 24028 2 Co
3、mmittees 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 Trade
4、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 publication Amd.
5、No. Date CommentsBSISO5725-4:1994 BSI 11-1999 i Contents Page Committees responsible Inside front cover National foreword ii Foreword iv Text of ISO 5725-4 1BSISO5725-4:1994 ii BSI 11-1999 National foreword This British Standard reproduces verbatim ISO5725-4:1994 and implements it as the UK national
6、 standard. Parts 1 to 6 of BS ISO5725 together supersede BS5497-1:1987 which will be withdrawn upon the publication of BS ISO5725-5. This British Standard is published under the direction of the Management Systems Sector Board whose Technical Committee QMS/16 has the responsibility to: aid enquirers
7、 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 Standards, as we
8、ll 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 British S
9、tandard 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, theISO title page, pages ii to iv, pages 1 to 22, an inside back cover and abackcover. This standard has been updated (see copyright date)
10、 and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.ISO5725-4:1994(E) ii BSI 11-1999 Contents Page Foreword iv Introduction 1 1 Scope 1 2 Normative references 2 3 Definitions 2 4 Determination of the bias of a standard measurement method
11、 by an interlaboratory experiment 2 4.1 The statistical model 2 4.2 Reference material requirements 2 4.3 Experimental design considerations when estimating the bias of a measurement method 3 4.4 Cross-references to ISO5725-1 and ISO5725-2 3 4.5 Required number of laboratories 3 4.6 Statistical eval
12、uation 3 4.7 Interpretation of the results of the statistical evaluation 3 5 Determination of the laboratory bias of one laboratory using a standard measurement method 5 5.1 Carrying out the experiment 5 5.2 Cross-references to ISO5725-1 and ISO5725-2 6 5.3 Number of test results 6 5.4 Choice of ref
13、erence materials 6 5.5 Statistical analysis 6 6 The report to, and the decisions to be taken by, the panel 7 6.1 Report by the statistical expert 7 6.2 Decisions by the panel 7 7 Utilization of trueness data 7 Annex A (normative) Symbols and abbreviations used in ISO5725 8 Annex B (informative) Exam
14、ple of an accuracy experiment 10 B.1 Description of the experiment 10 B.2 Precision assessment 10 B.3 Trueness assessment 11 B.4 Further analysis 11 Annex C (informative) Derivation of equations 20 C.1 Equations (5) and (6) (see4.5) 20 C.2 Equations (19) and (20) (see5.3) 22 Annex D (informative) Bi
15、bliography Inside back cover Figure B.1 Manganese content in iron ores: Test results at level 1 14 Figure B.2 Manganese content in iron ores: Test results at level 2 15 Figure B.3 Manganese content in iron ores: Test results at level 3 16 Figure B.4 Manganese content in iron ores: Test results at le
16、vel 4 17 Figure B.5 Manganese content in iron ores: Test results at level 5 18 Figure B.6 Manganese content in iron ores: h values grouped by laboratories 19 Figure B.7 Manganese content in iron ores: k values grouped by laboratories 19 Figure B.8 Manganese content in iron ores: Repeatability and re
17、producibility standard deviations as linear functions of the concentration level m 20ISO5725-4:1994(E) BSI 11-1999 iii Page Table 1 Values showing the uncertainty in the estimate of the bias of the measurement method 4 Table B.1 Manganese content in iron ores: Accepted reference values 11 Table B.2
18、Manganese content in iron ores: Analytical results as percentage Mn 11 Table B.3 Manganese content in iron ores: Laboratory means and laboratory variances 12 Table B.4 Manganese content in iron ores: Outliers and stragglers 13 Table B.5 Manganese content in iron ores: Estimation of repeatability and
19、 reproducibility standard deviations and bias of the measurement method 13ISO5725-4:1994(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 no
20、rmally 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
21、 the work. ISO collaborates closely with the International 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
22、requires approval by at least 75 % of the member bodies casting a vote. International Standard ISO5725-4 was prepared by Technical Committee ISO/TC 69, Applications of statistical methods, Subcommittee SC 6, Measurement methods and results. ISO5725 consists of the following parts, under the general
23、title Accuracy (trueness and precision) of measurement 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 measu
24、rement method; Part 4: Basic methods for the determination 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 ISO5725 together cancel and re
25、place ISO5725:1986, which has been extended to 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 ISO5725. Annex B, Annex C andAnnex D are for information only.I
26、SO5725-4:1994(E) BSI 11-1999 1 Introduction 0.1 ISO5725 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.
27、“Precision” refers to the closeness of agreement between test results. 0.2 General consideration of these quantities is given in ISO5725-1 and so has not been repeated in this part of ISO5725. ISO5725-1 should be read in conjunction with all other parts of ISO5725, including this part, because it gi
28、ves the underlying definitions and general 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
29、 an accepted reference value for the 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 b
30、e investigated by comparing the accepted 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
31、of one element interferes with the determination of another. 0.4 Two measures of trueness may be of interest and both are considered in this part of ISO5725. a) Bias of the measurement method: where there is a possibility that the measurement method may give rise to a bias, which persists wherever a
32、nd whenever the measurement is done, then it is of interest to investigate the “bias of the measurement method” (as defined in ISO5725-1). This requires an experiment involving many laboratories, very much as described in ISO5725-2. b) Laboratory bias: measurements within a single laboratory can rev
33、eal the “laboratory bias” (as defined in ISO5725-1). 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
34、vary; the method described in ISO5725-6 may be used for this. 1 Scope 1.1 This part of ISO5725 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 mea
35、surements on a continuous scale 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 me
36、asurements are to be carried out 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,
37、there is an implication that the same characteristic is being measured in exactly the same way. 1.5 This part of ISO5725 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 ref
38、erring to a reference measurement 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 measurement
39、s using an alternative measurement method whose bias is known to be negligible. 1.6 This part of ISO5725 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
40、 property (i.e. it does not consider interferences). Comparison of the trueness of two measurement methods is considered in ISO5725-6. NOTE 1In this part of ISO5725, bias is considered only at one level at a time. Therefore the index j for the level has been omitted throughout.ISO5725-4:1994(E) 2 BS
41、I 11-1999 2 Normative references The following standards contain provisions which, through reference in this text, constitute provisions of this part of ISO5725. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on t
42、his part of ISO5725 are 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 ge
43、neral statistical terms. 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
44、 and reproducibility of a standard measurement method. 3 Definitions For the purposes of this part ISO5725, the definitions given in ISO3534-1 and in ISO5725-1 apply. The symbols used in ISO5725 are given inAnnex A. 4 Determination of the bias of a standard measurement method by an interlaboratory e
45、xperiment 4.1 The statistical model In the basic model described in subclause 5.1 of ISO5725-1:1994, 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 th
46、e between-laboratory 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 in4.2.1 and4.2.2 shall be satisfied. Reference materials shall be homog
47、eneous. 4.2.1 Choice 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 experi
48、ment, a series 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 s
49、tandard measurement 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 con
