To Örebro University

We propose a new statistical method for analyzing data from a key comparison when two transfer standards are measured in two petals. The approach is based on a generalization of the classical random effects model, a popular procedure in metrology. A Bayesian treatment of the model parameters as well as of the random effects is suggested. The latter can be viewed as potential laboratory effects which are assessed through the proposed analysis. While the prior for the laboratory effects naturally is assigned as a Gaussian distribution, the Berger & Bernardo reference prior is taken for the remaining model parameters. The results are presented in terms of the posterior distributions derived for the laboratory effects. From these distributions posterior means and credible intervals are calculated. The proposed method paves the way for applying the established random effects model also for data arising from the measurement of several transfer standards in several petals, and it is illustrated for measurements of two 500mg transfer standards carried out in key comparison CCM.M-K7.