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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: Proposal for linking the results of CIPM and RMO key comparisons
Author(s): C. Elster, A. Link and W. Wöger
Journal: Metrologia
Year: 2003
Volume: 40
Issue: 4
Pages: 189
DOI: 10.1088/0026-1394/40/4/308
Web URL: http://stacks.iop.org/0026-1394/40/i=4/a=308
Tags: 8.42,KC
Abstract: A procedure for linking the results of a Regional Metrology Organisation (RMO) key comparison to those of a related Comité International des Poids et Mesures (CIPM) key comparison is proposed. The RMO results are linked to the CIPM results by a factor which is determined as the ratio of the CIPM key comparison reference value and the weighted mean of the RMO results of the linking laboratories. Correlations of the results of the linking laboratories in the two comparisons are taken into account. The uncertainties associated with the linked RMO results and the degrees of equivalence (DOEs) are explicitly given. The influence of correlations of the results of the linking laboratories in both comparisons is examined. It is shown that these correlations can decrease the linking uncertainty, whereas DOEs are expected to be influenced less. The proposed linking procedure is illustrated by its application to linking the results of a recent CIPM key comparison on accelerometer calibrations to that of a corresponding RMO key comparison.

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