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Accreditation and Quality Assurance: Journal for Quality, Comparability and Reliability in Chemical Measurement (v.14, #7)
Ensuring the potential for an intended quality of a measurement result must be done before and during the measurement, not after it (when it is too late)
by Paul De Bièvre (pp. 351-352).
The role of the sample standard deviation in the analysis of measurement data by Robin Willink (pp. 353-358).
This paper builds on recent letters to the editor to consider different ways in which the ‘sample standard deviation’ of a set of repeated measurements might be used in the expression of accuracy or uncertainty. A distinction is made between using the sample standard deviation, s, to calculate a figure of merit for the measurement procedure and using s to express uncertainty in the estimate of a measurand. In particular, we consider whether s should be adjusted for bias. It is shown that most procedures involving s are valid without the application of any such adjustment. The paper emphasizes the importance of clear definitions and an unambiguous statement of purpose, and also emphasizes the need for a distinction in notation between a random variable and its observed value.
Keywords: Accuracy; Error analysis; Repeatability; Reproducibility; Sample variance; Uncertainty
Assessing publically financed metrology expenditure against economic parameters by Nikola Poposki; Nineta Majcen; Philip Taylor (pp. 359-368).
The objective of this paper is to provide an economic perspective to those involved in public financing of the national metrology infrastructure. Whereas justifications for subsidising the national metrological activities are often historically biased, we raise the importance of economic considerations, which could be used during prioritisation. The expenditure in measurement and metrology infrastructure of European countries are compared to economic indicators for quality of life. Various proxies are used, such as measuring instruments sale (for measurement infrastructure) and data from the BIPM’s KCDB (as a proxy for national standards). As the EU Internal Market also holds for the provision of metrological services, the paper exposes possible trends regarding public financing to the sector.
Keywords: Measurements; Metrology infrastructure; Public good
Computer-simulation data inclusive regression modelling in measurement by Vladimir B. Bokov (pp. 369-379).
Measurement involves the determination of quantitative estimates of physical quantities from experiment, along with estimates of their associated uncertainties. Herewith an experimental system model is the key to extracting information from experimental data. With this concern novel regression modelling techniques have been fashioned by data combination from designed computer-simulation and physical experiments. These techniques have allowed attaining the advanced level of model completeness and precision via approximation of the true unknown model by mathematical product of appropriate theoretical and empirical functions. Pneumatic gauge candidate models’ building, solving and validation revealed that computer-simulation data inclusive response surface models permit to attain minimum discrepancy from empirical evidence.
Keywords: Theoretical model; Experimental design; Physical experiment
Measurement uncertainty of shikimic acid in red wines produced in Chile by Catherine Tessini; Claudia Mardones; Lorena Rivas; Dietrich von Baer (pp. 381-387).
High-performance liquid chromatography (HPLC) to determine shikimic acid is used as a complementary tool to differentiate wine varieties. In order to correctly classify, measurement uncertainty of shikimic acid by HPLC in red wine was estimated considering the following components: uncertainty associated with the preparation of shikimic acid stock solution, uncertainty associated with quantification using a calibration curve, and uncertainty associated with precision. The most important contribution to total uncertainty was the method precision. The expanded uncertainty (U) for different wine varieties was between 2.6 and 8.5%. The method was applied to determine the concentration of shikimic acid in different emerging wine varieties cultivated in Chile, such as Carmenère, Shiraz, and Pinot Noir, comparing them with classical varieties, such as Cabernet Sauvignon and Merlot. Shiraz wines presented lower shikimic acid concentrations (between 27 and 86 mg L−1 with U (k=2) = 2.6%) than Cabernet Sauvignon wines (between 41 and 142 mg L−1 with U (k=2) = 8.1%), but their concentrations were higher than found in Merlot (from 9 to 41 mg L−1 with U (k=2) = 4.3%) and Carmenère wines (between 7 and 49 mg L−1 with U (k=2) = 5.8%). Pinot Noir was the variety with the lowest concentration of this acid (7–14 mg L−1 with U (k=2) = 8.5%).
Keywords: HPLC; Red wine; Shikimic acid; Measurement uncertainty
Estimation in multiple measurements by Walter Bich (pp. 389-392).
A recent paper by Nam et al. (Accred Qual Assur 14:43–47, 2009) considers the issue of repeated measurements of a same measurand. The paper is a follow-up of two previous papers (Choi et al. in Accred Qual Assur 8:13–15,
Keywords: 2003, 8:205–207, 2003) on the same topic. The first two papers show a well-known fact, i.e., that systematic effects are not reduced by repeating measurements, and give formulae for the uncertainty of the estimate of the average from repeated measurements in the case that the differences between individual results are not (Choi et al. in Accred Qual Assur 8:13–15, 2003) or are (Choi et al. in Accred Qual Assur 8:205–207, 2003) statistically significant, respectively. The last paper addresses a more interesting issue, that is, a difference in the estimate average for non-linear models depending on how raw data is processed in the model. In the present paper, I re-discuss the whole issue of multiple measurements, trying to clarify the various aspects of the topic.
Measurement traceability and US IVD manufacturers: the impact of metrology by Dave Armbruster (pp. 393-398).
A goal of clinical laboratory science is to produce accurate and comparable patient test results for a specimen independent of analytical methodology. The In Vitro Diagnostics Directive in Europe has provided the impetus for the U.S. in vitro diagnostic (IVD) industry to adapt the concepts of Metrology, the science of measurement, including measurement traceability and measurement uncertainty. The joint committee for traceability in laboratory medicine has provided a valuable database of internationally recognized reference materials and methods and reference laboratories. Much of the responsibility for measurement traceability falls on IVD manufacturers, but all global stakeholders, including the clinical laboratory profession, government Regulatory bodies, metrology institutes, and the providers of EQA/PT surveys, must cooperate to progress toward this goal. The adaptation of the concepts of Metrology to the clinical laboratory is an appropriate and logical development and it will continue in the twenty-first century.
Keywords: Traceability; Reference materials; Reference methods; JCTLM; Assay standardization
Validation of specificity in doping control: problems and prospects
by Nicolaas (Klaas) M. Faber (pp. 399-399).