Analysis and linking of international measurement comparisons

We present a method to analyse international measurement comparisons, including linking two or more comparisons. This method, which is based on linear generalized least-squares estimation, directly gives the degrees of equivalence required by the Mutual Recognition Arrangement, both relative to the key comparison reference value (KCRV) and between pairs of participating laboratories. The key features of the method are its ability to accommodate multiple travelling standards (including instabilities in the standards), multiple measurements by participating laboratories, multiple comparison loops, and known correlations between measurements (both intra- and interlaboratory). The method can be applied with or without a KCRV (but does not give a value for the KCRV). An analysis of the linked comparisons APMP.M.M-Kl and CCM.M-Kl is presented to illustrate the method. While best suited to comparisons with single-valued travelling standards, the method can be applied to most other comparison types.