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1.
M. Golze 《Accreditation and quality assurance》1998,3(6):227-230
The general requirement of Quality Management standards to include in test reports a statement of the uncertainty of the
results reflects the fact that a test result is rather useless without a knowledge of its accuracy. After an outline of the
basic concepts of uncertainty, the need for uncertainty statements is illustrated for different ranges of applications.
Received: 23 December 1997 · Accepted: 3 March 1998 相似文献
2.
W. Bremser 《Accreditation and quality assurance》1998,3(10):398-402
The principles of uncertainty-based data evaluation are explained. Based on a brief review of recent publications on the
topic, examples for application to standard procedures in analytical chemistry – calibration, method validation, standard
addition etc., – are given. The performance and the advantages of uncertainty-based data evaluation are discussed.
Received: 4 July 1998 · Accepted: 6 July 1998 相似文献
3.
Introducing the concept of uncertainty of measurement in testing in association with the application of the standard ISO/IEC 17025 总被引:1,自引:0,他引:1
N. Mueller 《Accreditation and quality assurance》2002,7(2):79-80
ISO/IEC 17025 requests laboratories to estimate the overall uncertainty associated with a test result. In many cases this
means a new requirement to laboratories. It is essential to understand the importance of the knowledge of the uncertainty
of measurements as well as the principle that not always the smallest possible uncertainty is needed, but fitness for purpose
has to be achieved. The paper suggests a policy on the implementation of the concept of uncertainty and guidance on how to
proceed, taking into account the present state of the art of understanding the problem. 相似文献
4.
An approach for uncertainty evaluation is proposed to determine the overall uncertainty by combining the uncertainties of
the individual results from multiple measurements. It is accomplished by the separate combinations of the individual random
and systematic components of the uncertainties of the individual results. The approach is useful when the individual results
are not statistically different. It is recognized that, owing to the correlation, the uncertainty resulting from systematic
effects is not reduced by multiple measurements. On the contrary, the uncertainty resulting from random effects can be reduced.
Received: 3 May 2002 Accepted: 16 July 2002 相似文献
5.
6.
We review the draft international standard ISO/IEC 17025 and the EA guidelines; and present the existing National Physical
Laboratory publication “Software in scientific instruments” and the new Measurement System Validation Best Practice guide.
Received: 2 November 1999 / Accepted: 29 January 2000 相似文献
7.
Dean A. Flinchbaugh L. F. Crawford David Bradley 《Accreditation and quality assurance》2001,6(12):493-500
A model is presented that correlates historical proficiency test data as the log of interlaboratory standard deviations versus
the log of analyte concentrations, independent of analyte (measurand) or matrix. Analytical chemistry laboratories can use
this model to set their internal measurement quality objectives and to apply the uncertainty budget process to assign the
maximum allowable variation in each major step in their bias-free measurement systems. Laboratories that are compliant with
this model are able to pass future proficiency tests and demonstrate competence to laboratory clients and ISO 17025 accreditation
bodies. Electronic supplementary material to this paper can be obtained by using the Springer LINK server located at http://dx.doi.org/
10.1007/s007690100398-y.
Received: 31 March 2001 Accepted: 11 September 2001 相似文献
8.
J. Pauwels A. van der Veen A. Lamberty H. Schimmel 《Accreditation and quality assurance》2000,5(3):95-99
Certification of reference materials is far more than just characterisation of a selected homogeneous batch of material.
From the perspective of the ISO Guide on the Expression of Uncertainty in Measurement (GUM) all uncertainty sources relevant
to the user of an individual certified reference material (CRM) sample at a moment in time should be part of the CRM uncertainty.
This not only includes the full uncertainty of the batch characterisation (rather than the statistical variation), but also
all uncertainties related to possible between-bottle variation, instability upon long-term storage and instability during
transport to the customer.
Received: 21 April 1999 · Accepted: 24 September 1999 相似文献
9.
Methods recommended by the International Standardization Organisation and Eurachem are not satisfactory for the correct estimation
of calibration uncertainty. A novel approach is introduced and tested on actual calibration data for the determination of
Pb by ICP-AES. The improved calibration uncertainty was verified from independent measurements of the same sample by demonstrating
statistical control of analytical results and the absence of bias. The proposed method takes into account uncertainties of
the measurement, as well as of the amount of calibrant. It is applicable to all types of calibration data, including cases
where linearity can be assumed only over a limited range.
Received: 25 August 2001 Accepted: 21 December 2001 相似文献
10.
Jane Beaumont 《Accreditation and quality assurance》1999,4(1-2):39-42
The requirements for establishing the competence of organisations involved in testing, calibration, certification and inspection,
and the criteria for their assessment and accreditation are specified in international guides and European standards. As these
guides and standards are intended for use by a range of organisations and accreditation bodies, operating in different disciplines,
they are written in general terms in order to be widely applicable. It follows that some interpretation of the requirements
is needed in order to address the different ways in which both organisations and accreditation bodies operate. This may be
seen by accredited organisations as providing an opportunity for accreditation bodies to 'change the goalposts'; the needs
of these organisations and of their clients must be accommodated as far as possible, without diminishing the value of, or
undermining confidence in, accreditation. The United Kingdom Accreditation Service has been listening to its customers, reviewing
its activities and is offering a more flexible pragmatic approach to assessment and accreditation; some of the new developments
are described. 相似文献
11.
G. I. Ramendik 《Accreditation and quality assurance》1999,4(5):211-213
The structure and activities of a new accreditation body called the Russian Union of Measurement Accreditation Systems (RUMAS)
are briefly described. 相似文献
12.
M. H. Ramsey 《Accreditation and quality assurance》2002,7(7):274-280
Appropriate sampling, that includes the estimation of measurement uncertainty, is proposed in preference to representative
sampling without estimation of overall measurement quality. To fulfil this purpose the uncertainty estimate must include contribution
from all sources, including the primary sampling, sample preparation and chemical analysis. It must also include contributions
from systematic errors, such as sampling bias, rather than from random errors alone. Case studies are used to illustrate the
feasibility of this approach and to show its advantages for improved reliability of interpretation of the measurements. Measurements
with a high level of uncertainty (e.g. 50%) can be shown to be fit for some specified purposes using this approach. Once reliable
estimates of the uncertainty are available, then a probabilistic interpretation of results can be made. This allows financial
aspects to be considered in deciding upon what constitutes an acceptable level of uncertainty. In many practical situations
”representative” sampling is never fully achieved. This approach recognises this and instead, provides reliable estimates
of the uncertainty around the concentration values that imperfect appropriate sampling causes.
Received: 28 December 2001 Accepted: 25 April 2002 相似文献
13.
A. Maroto Ricard Boqué Jordi Riu F. Xavier Rius 《Accreditation and quality assurance》2002,7(3):90-94
The bias of an analytical procedure is calculated in the assessment of trueness. If this experimental bias is not significant,
we assume that the procedure is unbiased and, consequently, the results obtained with this procedure are not corrected for
this bias. However, when assessing trueness there is always a probability of incorrectly concluding that the experimental
bias is not significant. Therefore, non-significant experimental bias should be included as a component of uncertainty. In
this paper, we have studied if it is always necessary to include this term and which is the best approach to include this
bias in the uncertainty budget. To answer these questions, we have used the Monte-Carlo method to simulate the assessment
of trueness of biased procedures and the future results these procedures provide. The results show that non-significant experimental
bias should be included as a component of uncertainty when the uncertainty of this bias represents at least a 30% of the overall
uncertainty.
Received: 29 May 2001 Accepted: 10 December 2001 相似文献
14.
Study of the uncertainty in gravimetric analysis of the Ba ion 总被引:3,自引:0,他引:3
The determination of barium by the gravimetric method, in which the precipitation of BaSO4 was formed and weighed, coupled with instrumental measurement of trace constituents was studied. The analyte’s remaining
in the filtrate and washes, mechanical loss, contaminants in the precipitate are the main influencing factors of uncertainty.
A series of condition tests have been done, to reduce the effect of the factors mentioned above and the optimum test condition
was found. The determination was carried out with a strictly defined operational procedure. The trace amounts of barium in
the filtrate, washes and mechanical loss were determined by ICP-AES, the chloride occluded in the precipitate was determined
by ion chromatography (IC), calculated as BaCl2 and barium, and sodium by FAAS, calculated as Na2SO4. The average mass of barium in the filtrate contributes about 0.06% relative to that of the total barium, in washes about
0.09%, mechanical loss about 0.06%, contaminants of BaCl2 about 0.08% and Na2SO4 about 0.05%. All the trace constituents were determined and corrected on a sample-by-sample basis. Sources of uncertainty
were assessed thoroughly. The uncertainty of this combined gravimetric-instrumental method was improved remarkably compared
with that of gravimetric method alone. The expanded uncertainty (k =2) is 0.08%.
Received: 15 June 2000 Accepted: 25 December 2001 相似文献
15.
H. Andersson 《Accreditation and quality assurance》2002,7(6):228-233
When a test is performed in order to qualify a material or a product for a certain use, the result is generally compared with
an acceptance limit. The test result has an uncertainty which should be estimated and stated (e.g. in accordance with GUM).
Very often this is not the case. Further, discussions often arise on the issue of how the uncertainty shall be considered
in relationship to the acceptance limit. The intention of this note is to describe, in simple terms, the statistical background
and to give some recommendations. In short, there are two clean-cut, extreme situations. The first case is when the uncertainty
of the testing procedure is the dominating factor. Here it is found that the estimates of single laboratories cannot, generally,
be used for comparisons with acceptance limits. One should have standardised, well-verified estimates based on comprehensive
investigations of the method. It can also be concluded that comparisons between test results and acceptance limits have to
be made with regard to the actual circumstances, as, e.g. how the acceptance limit is related to the risk. In the second case,
the variation in the property of the material or product dominates and the uncertainty of the testing procedure is negligible.
When the results are non-quantitative (go – no go), statistical methods can be used to estimate the risk taken with a certain
sampling and acceptance strategy that a certain proportion of the batch to be delivered does not qualify. This should be considered
more often in standardisation of product test methods. When the results are quantitative, a statistical analysis should be
performed and the uncertainty should be compared with the acceptance limit as before, from the actual circumstances. When
effects of testing uncertainty and product variation are comparable a sound treatment requires extensive experimental work.
No short cuts can be made without loss of confidence!
Received: 17 August 2001 Accepted: 21 March 2002 相似文献
16.
A concise graphical depiction, the “onion” chart, is described for presenting uncertainty budgets for any measurand, y, having a set of component variances, . The onion chart consists of a concentric series of rings. Each ring is constructed from the set of fractional contributions, . The outer ring includes all and depicts the combined standard uncertainty, u
c
(y), where u
c
2(y) ≡ ∑u
i
2(y). Moving inward, each successive ring deletes the largest remaining . A “reduced” is calculated for that ring from the remaining set of , with the fractional contributions calculated using the “reduced” . This format facilitates rapid visual comparison of the importance of each component, with minor components becoming visible as the larger components are successively deleted. An example is presented using data from pH metrology, including the physical interpretation of the resulting diagram. 相似文献
17.
W. van Deijck 《Accreditation and quality assurance》1996,1(5):197-200
Since the late 1980s, much attention has been paid to the usefulness of ISO-9000 certification. At present more than 45000
companies and institutions worldwide have been granted an ISO-9000 certificate. In the field of quality assurance, however,
the ISO-9000 series does not completely cover the aspect of traceability. Demonstrable traceability is a particular problem
in quality assurance of products by chemical analysis. In this paper realisation of demonstrable traceability is discussed,
using the field of gas analysis as an example. Attention is focused on the usefulness of accreditation for laboratories performing
quality assurance analyses. The basic question is asked whether and, if so, when accreditation is worth the trouble in cases
where demonstrable traceability is required.
Received: 15 February 1996 Accepted: 6 March 1996 相似文献
18.
John L. Love 《Accreditation and quality assurance》2002,7(3):95-100
Chemical results normally involve traceability to two reference points, the specific chemical entity and the quantity of this
entity. Results must also be traceable back to the original sample. As a consequence, any useful estimation of uncertainty
in results must include components arising from any lack of specificity of the method, the variation between repeats of the
measurement and the relationship of the result to the original sample. Chemical metrology does not yet incorporate uncertainty
arising from any lack of specificity from the method selected or the traceability of the result to the original sample. These
sources of uncertainty may however have much more impact on the reliability of the result than will any uncertainty associated
with the repeatability of the measurement. Uncertainty associated with sampling may amount to 50–1000% of the reported result.
Chemical metrology must be expanded to include estimations of uncertainty associated with lack of specificity and sampling.
Received: 29 May 2001 Accepted: 17 December 2001 相似文献
19.
The problem with which analytical laboratories are confronted, after traceability of their results has been demonstrated, is correctly estimating their uncertainty– to which traceability is also to some extent subject. While the general principles for calculating the uncertainty of physical
measurements are applicable to chemical metrology, some refinements are needed, especially careful selection and planning
the level at which uncertainty will be estimated by each laboratory in accordance with its capacity and required demands.
Depending on the particular decision to be made, the mechanism to be used to estimate the uncertainty varies markedly; also,
the rigour of the estimation increases with increasing stringency of the demands. This paper describes the primary sources
of uncertainty in chemical metrology and discusses different approaches to its estimation in relation to the type of analytical
laboratory concerned. The view presented tries to be close to the bench analytical level, in order to be practical and flexible
for laboratories, although it could sometimes be considered slightly heterodox.
Received: 25 March 1997 · Accepted: 20 September 1997 相似文献
20.
L. K. Isaev V. M. Lakhov Y. A. Karpov I. V. Boldyrev B. I. Paneva G. I. Fridman 《Accreditation and quality assurance》1999,4(5):169-173
The history and the present state of the national system for accreditation of analytical laboratories in Russia are described.
Received: 1 September 1998 / Accepted: 1 September 1998 相似文献