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Analysis of key comparisons

Working Group 8.42


Key comparisons are interlaboratory comparisons carried out regularly between National Metrology Institutes (NMIs) within the framework of the CIPM Mutual Recognition Arrangement (Opens external link in new windowMRA). Key comparisons enable the mutual recognition of calibrations, measurements, and test certificates of the NMIs and mark a major step in supporting international trade, commerce and regulatory affairs. The final report and the supporting technical data of each key comparison are stored and made publicly available at the key comparison data base  Opens external link in new windowKCDB of the Bureau International des Poids et Mesures (Opens external link in new windowBIPM). Fig. 1 shows a typical example of key comparison data.

Fig.1 Example data of a key comparison along with the key comparison reference value (KCRV). The blue results indicate control measurements made by the so-called pilot laboratory.


The analysis of key comparisons can be seen as a Opens external link in new windowMeta-Analysis in which the results reported by the participating laboratories are assessed. Fixed effects or random effects models are popular models applied in meta-analysis. One focus of research of PTB’s Working Group 8.42 is the development of Bayesian methods for the estimation of fixed and random effects models. This includes the assignment of vaguely informative or appropriate non-informative priors and the exploration of the properties of the resulting inference. Other topics of research are situations in which the common measurand shows a drift, or where the explanatory power of key comparisons is assessed in dependence on the stability of the common measurand and the uncertainties reported by the participating laboratories.



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Title: Model-based analysis of key comparisons applied to accelerometer calibrations
Author(s): C. Elster, A. Link and H.-J. von Martens
Journal: Measurement Science and Technology
Year: 2001
Volume: 12
Issue: 10
Pages: 1672
DOI: 10.1088/0957-0233/12/10/308
Web URL: http://stacks.iop.org/0957-0233/12/i=10/a=308
Tags: 8.42,KC
Abstract: The concept of a model-based analysis of key comparisons is proposed and illustrated by applying it to data from a regional key comparison of accelerometer calibrations on a scale of frequencies. A physical model of the frequency dependence of the accelerometers' sensitivities is used to calculate reference values. The parameters of the physical model are determined by weighted least squares, and the resulting model is shown to conform with the data. Uncertainties associated with the reference values calculated by the physical model are smaller than those associated with reference values obtained by standard analysis. This can lead to a more favourable assessment of the degree of equivalence of single laboratory measurement values as expressed by calculated E n -numbers. The degree of equivalence of single laboratory measurement values is quantitatively calculated by both model-based analysis and standard analysis, and the results obtained and their differences are discussed.

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