Abstract. On the basis of main provisions of ISO standards, reproducibility and repeatability in determination of measured characteristics of. Buy ISO ACCURACY (TRUENESS AND PRECISION) OF MEASUREMENT METHODS AND RESULTS – PART 6: USE IN PRACTICE OF. INTERNATIONAL STANDARD ISO ISO/TC 69, Applications of statistical methods, Subcommittee SC 6, Measurement methods.
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Unless otherwise specified, no part of this publrcation may be reproduced or utrlized In any form or by any means, electronrc or mechanical, rncludrng photocopyrng and mrcrofilm, wrthout permission in 5725–6 from the publisher.
ISO Accuracy of Measurement Methods and Results Package
C Derivation of equations The work of preparing International Standards is jso carried out through IS0 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. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. IS0 consists of the following parts, under the general title Accuracy trueness and precision of measurement methods and results: General principles and definitions – Part 2: Basic method for the determination of repeatability and re- producibility of a standard measurement method – Part 3: Intermediate measures of the precision of a standard measurement method – Part 4: Basic methods io the determination of the trueness of a standard measurement method – Ixo 5: Alternative methods for the determination of the precision of a standard measurement method – Part 6: Annex A forms an integral part of this part of IS0 Annexes B, C and D are for information only.
IS0 l should be read in conjunction with all other parts of IS0including this part, because it gives the underlying definitions and general principles. Al- though, for some measurement methods, the true value cannot be known exactly, it may be possible to have an accepted reference value for the property being measured; for example, if suitable reference materials sio available, or if the accepted reference value can be established by refer- ence to another measurement method or by preparation of a known sample.
The trueness of the measurement method can be investigated by comparing isl 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 of one element interferes with the determination of another. This requires an experiment involving many ieo, very much as described in IS0 If it is proposed to undertake an experiment to estimate laboratory bias, then it should be realized that the estimate will be isk only at the time of the ex- periment.
Further regular testing is required to show that the labora- tory bias does not vary; the method described in IS0 may be used for this. Basic methods for the determination of the trueness of sio standard measurement method iao Scope 1.
All measurements are to be carried out according to that standard method. When a value for the bias of a measure- ment method is quoted, together with a test result obtained by that method, 57256 is an implication that the same iwo is being measured in exactly the same way. 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- ment method whose bias is known to be negligi- ble.
It is not applicable if the bias in the measurement of one property is affected by the level of a second property i. Comparison of the trueness of two measurement methods is considered in IS0 Therefore the Index j for the level has been omitted throughout.
Sio standards are subject to revision, and parties to agreements ios on this part of IS0 are encouraged to investigate the possibility of applying the most recent editions of the standards izo below. IAccuracy trueness and precision of measurement methods and results – Part 1: Ido principles and definitions. Basic method for the uso of repeatability and re- producibility of a standard measurement method.
The symbols used in IS0 are given in annex A. Here B is the laboratory component of bias, i. Reference materials shall be homogeneous. In some cases it will be important to include, in the assessment exper- iment, a series of reference materials, each corre- sponding 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 measurement method, e.
There are three cases, as follows. Relevant International Standards on sample division should be consulted. The units should be selected on a random basis for distribution. If the measurement process is non-destructive, it is poss- ible to give all the laboratories in the interlaboratory experiment the same unit of reference material, but this will extend the time-frame of the experiment.
If the bias is found to be statistically insignif- icant, then the objective is to determine the magnitude of the maximum bias that would, with a certain probability, remain undetected by the results of 57256- experiment. The differences are a there is an additional requirement to use an ac- cepted reference value, and b the number of participating laboratories and the number of test results shall also satisfy the re- quirements given in 4.
The number of laboratories to be used is discussed in subclause 6.
A guide to oso ing how many is given below. In order for the results of an experiment to be able to detect with a high probability see annex Cl a prede- termined magnitude of bias, the minimum number oso laboratories, p, and test results, n, shall satisfy the following equation: However, for practical reasons, the choice of the number of laboratories is usually a compromise between the availability of re- sources and the desire to reduce the value is 6, to a satisfactory level.
If the reproducibility of the measurement method is poor, then it will not be practical to achieve a high degree of certainty in the estimate of the bias. When gR is larger than T. In particular, if outlying values are de- tected, all necessary steps shall be taken to investi- gate the reasons why they have been obtained, including re-appraisal of the suitability of the accepted reference value.
Equations 8 to 10 as- sume an equal number n of test results in each laboratory. If io is not true, the respective equations given in IS0 should be used to calculate s.
If the repeatability standard deviation of the standard measurement method has not been previously deter- mined in accordance with IS0s, will be con- sidered to be the best estimate of it. Unless otherwise stated, a is assumed to be 0. In the former case, the repeatability standard devi- ation, cr, will be used for the jso of the bias of the measurement method.
In the latter case, it is necessary to investigate the causes of the discrep- ancy and possibly to repeat the experiment prior to proceeding further. Unless otherwise stated, a is assumed to be 0, In the former case, the repeatability standard devi- ation, gr, and the reproducibility standard deviation, gR, will be used for the assessment of the trueness of the measurement method. In the latter case, a careful examination of the working conditions of each laboratory shall be carried out before the assessment of the bias of the standard measurement method is undertaken.
It may appear that some laboratories did not use the required equipment or did not work ac- cording to the specified conditions. In chemical anal- ysis, problems may arise from, for example, insufficient control of temperature, moisture, pres- ence of contaminants, etc.
As a result the experiment may have to be repeated to yield the expected preci- sion values. The variation of the estimate of the bias of the measurement method is due to the variation 5752-6 the results of the measurement process and is expressed by its standard deviation computed as in the case of known precision values, or siJzT-yF .
Prior to conducting the as- sessment of trueness, a check of the precision of the standard measurement method as applied by the lab- oratory shall be performed. This implies comparison between the within-laboratory standard deviation and the stated repeatability standard deviation of the standard measurement method.
BS ISO 5725-6:1994
Apart from the restriction to a single laboratory. If the repeatability of the measurement method is poor, then it will not be practical to achieve a high degree of certainty in the estimate of the bias of the laboratory. If the repeatability standard deviation, or, of the stan- dard measurement method is known, the estimate s, can be assessed by the following procedure.
The uncertainty in the estimate of the laboratory bias depends on the repeatability of the measurement method and on the number of test results obtained. A Awar G 1, In the former case, the repeatability standard devi- ation of the measurement method, or, will be used for the assessment of the laboratory bias.
ISO Accuracy of measurement methods and results-Part 2 Basic method – MBA智库文档
In the latter case, consideration should be given to repeating the experiment with verification at all steps that the standard measurement method is properly implemented. If u, is un- known, its estimate s. The laboratory bias is further considered in IS0 In this report the following information shall be given: What action should be taken with respect to re- jected outlying laboratories?
If so, what are the improvements required? Do the results of the accuracy experiment justify the acceptability of the measurement method for adoption as a standard? What action is to be taken concerning its publication? Utilization of trueness data Refer to clause 7 of IS0 Calibration-different Equipment-different Identifier for a particular laboratory Identifier for intermediate measures of precision; in brackets, identification of the type of intermediate situation ldentif ier for a particular level IS0 Each laboratory re- ceived two randomly selected bottles of test sample for each level and performed duplicate analyses on each bottle.
The purpose of the two-bottle system was to confirm the absence of the between-bottle variation. The analysis was performed such that in the case where the absence of between-bottle variation is confirmed, the four analytical results can be con- sidered as replicates under repeatability conditions. Analysis of the results showed that the between- bottle variation was indeed insignificant; the sample was considered to be homogeneous.
Thus results from each laboratory can be considered as replicates under repeatability conditions. The analytical results are listed in tableB.
The laboratory means and vari- ances for each of the five test materials are listed in table 8. The test results for each level are shown in figures B.
The boxed points in figures B. One laboratory re- sult was identified as a straggler; it originated from the same laboratory Lab. The h and k values are shown in figures B. The h values figureB. It was therefore decided to discard the results from laboratory 10 completely; it should be the object of special attention, and the matter should be resolved.
The k values figure B-7 show that laboratories There again, appropriate action should be taken by investigating these laboratories, or, if necessary, by tightening the protocol of the measurement method. The repeatability and the reproducibility standard de- viations were then computed excluding those data that were discarded.
The results of this computation are summarized in table B.