Several recent international comparison studies used a relatively novel experimental design to evaluate the measurement capabilities of participating organizations. These studies compared the values assigned by each participant to one or more qualitatively similar materials with measurements made on all of the materials by one laboratory under repeatability conditions. A statistical model was then established relating the values to the repeatability measurements; the extent of agreement between the assigned value(s) and the consensus model reflected the participants' measurement capabilities. Since each participant used their own supplies, equipment, and methods to produce and value-assign their material(s), the agreement between the assigned value(s) and the model was a fairer reflection of their intrinsic capabilities than provided by studies that directly compared time- and material-constrained measurements on unknown samples prepared elsewhere. A new statistical procedure is presented for the analysis of such data. The procedure incorporates several novel concepts, most importantly a leave-one-out strategy for the estimation of the consensus value of the measurand, model fitting via Bayesian posterior probabilities, and posterior coverage probability calculation for the assigned 95% uncertainty intervals. The benefits of the new procedure are illustrated using data from the CCQM-K54 comparison of eight cylinders of n-hexane in methane.

The 2010 CCQM-K79 'Comparison of value-assigned CRMs and PT materials: Ethanol in aqueous media' is the second key comparison directly testing the chemical measurement services provided to customers by National Metrology Institutes (NMIs) and Designated Institutes (DIs). CCQM-K79 compared the assigned ethanol values of proficiency test (PT) and certified reference materials (CRMs) using measurements made on these materials under repeatability conditions. Nine NMIs submitted 27 CRM or value-assigned PT materials for evaluation. These materials represent many of the higher-order reference materials then available for this commercially and forensically important measurand.The assigned ethanol mass fraction in the materials ranged from 0.1 mg/kg to 334 mg/kg. All materials were stored and prepared according the specifications provided by each NMI. Samples were processed and analyzed under repeatability conditions by one analytical team using a gas chromatography with flame ionization detection (GC-FID) method of demonstrated trueness and precision.Given the number of materials and the time required for each analysis, the majority of the measurements were made in two measurement campaigns ('runs'). Due to a shipping delay from one NMI, an unanticipated third campaign was required. In all three campaigns, replicate analyses (three injections of one preparation separated in time) were made for one randomly selected unit of each of the 27 materials. Nine of the 27 materials were gravimetrically diluted before measurement to provide solutions with ethanol mass fraction in the established linear range of the GC-FID method. The repeatability measurement value for each analyzed solution was estimated as the mean of all replicate values. The within- and between-campaign variance components were estimated using one-way ANOVA. Markov Chain Monte Carlo Bayesian analysis was used to estimate 95% level-of-confidence coverage intervals for the mean values.Uncertainty-weighted generalized distance regression was used to establish the key comparison reference function (KCRF) relating the assigned values to the repeatability measurements. On the basis of leave-one-out cross-validation, all of the assigned values for all 27 materials were deemed equivalent at the 95% level of confidence. These materials were used to define the KCRF.Parametric bootstrap Monte Carlo was used to estimate 95% level-of-confidence coverage intervals for the degrees of equivalence of materials, d ± U95(d), and of the participating NMIs, D ± U95(D). Because of the very wide range of ethanol mass fraction in the materials, these degrees of equivalence are expressed in percent relative form: %d ± U95(%d) and %D ± U95(%D). The median of the absolute values of the %D for the participating NMIs is less than 0.05% with a median U95(%D) of less than 1%. These results demonstrate that the participating NMIs have the ability to correctly value-assign CRMs and proficiency test materials for ethanol in aqueous media and similar measurands.Main text. To...

The Metrology Cloud has been described and implemented at some degree for several National Institutes of Metrology (NMI) or Designated Bodies, typically with emphasis in the Legal Metrology aspects, however, there is a lack of coverage for Scientific Metrology aspects. The paper first describes the situation at a specific NMI, then details the used procedure to find a solution and briefly provides examples for time conditioned properties, time dependent behavior, and virtual measuring instrument's simulated response, finally the results are revised, and future work is listed besides conclusion.

The 2009 CCQM-K80 'Comparison of value-assigned CRMs and PT materials: creatinine in human serum' is the first in a series of key comparisons directly testing the chemical measurement services provided to customers by National Metrology Institutes (NMIs) and Designated Institutes. CCQM-K80 compared the assigned serum creatinine values of certified reference materials (CRMs) using measurements made on these materials under repeatability conditions. Six NMIs submitted 17 CRM materials for evaluation, all intended for sale to customers. These materials represent nearly all of the higher-order CRMs then available for this clinically important measurand.The certified creatinine mass fraction in the materials ranged from 3 mg/kg to 57 mg/kg. All materials were stored and prepared according the specifications provided by each NMI. Samples were processed and analyzed under repeatability conditions by one analyst using isotope dilution liquid chromatography–mass spectrometry. The instrumental repeatability imprecision, expressed as a percent relative standard deviation, was 1.2%.Given the number of materials and the time required for each analysis, the measurements were made in two measurement campaigns ('runs'). In both campaigns, replicate analyses (two injections of one preparation separated in time) were made on each of two or three independently prepared aliquots from one randomly selected unit of each of the 17 materials. The mean value, between-campaign, between-aliquot and between-replicate variance components, standard uncertainty of the mean value, and the number of degrees of freedom associated with the standard uncertainty were estimated using a linear mixed model. Since several of the uncertainties estimated using this traditional frequentist approach were associated with a single degree of freedom, Markov Chain Monte Carlo Bayesian analysis was used to estimate 95% level-of-confidence coverage intervals, U95. Uncertainty-weighted generalized distance regression was used to establish the key comparison reference function (KCRF) relating the assigned values to the repeatability measurements. Parametric bootstrap Monte Carlo was used to estimate 95% level-of-confidence coverage intervals for the degrees of equivalence of materials, d ± U95(d), and of the participating NMIs, D ± U95(D). Because of the wide range of creatinine mass fraction in the materials, these degrees of equivalence are expressed in percent relative form: %d ± U95(%d) and %D ± U95(%D).On the basis of leave-one-out cross-validation, the assigned values for 16 of the 17 materials were deemed equivalent at the 95% level of confidence. These materials were used to define the KCRF. The excluded material was identified as having a marginally underestimated assigned uncertainty, giving it large and potentially anomalous influence on the KCRF. However, this material's %d of 1.4 ± 1.5 indicates that it is equivalent with the other materials at the 95% level of confidence. The median |%d| for all 17 of the materials is 0.3 with a med...