Statistical reassessment of calibration and measurement capabilities based on key comparison results

According to the CIPM Mutual Recognition Arrangement, a calibration and measurement capability (CMC) uncertainty for a laboratory offering a particular calibration or measurement service is normally expressed at a \SI{95}{\percent} level of confidence. When laboratories' CMC claims are unsupported by the relevant key comparison (KC), one option is for modified values to be assigned to their CMC uncertainties. In many cases when CMCs apply to a continuous interval of values such as mass concentration or wavelength, there is no directly relevant KC that can be used in support since KCs are carried out only for selected discrete values of the quantity concerned. Under realistic assumption, we developed a method that is applicable in such an instance and for which the reported CMC uncertainties are amplified so that they are underpinned by the results of the KC. The amplification factors depend on the laboratories' degrees of equivalence (DoEs) for these discrete values, and judiciously adjusted to achieve consistency with the key comparison reference values. The method is based on the patterns in the individual behaviour of the DoEs of the participating laboratories for the discrete values, implying the presence of correlation associated with the DoE values. It applies when the weighted mean of some or all of the measured values reported by the participating laboratories in the KC is used to obtain the KC reference value.