Modeling Outlying Labs in Inter-Laboratory Studies

Abstract:

Inter-laboratory studies� (especially so-called Key-Comparisons) are conducted to ensure measurement capability for commerce and to evaluate both national and international equivalence of measurement.��� In these studies, a reference value of some measurand (the underlying quantity subject to measurement) is computed and results for all labs are compared to this single value.�� How to determine the reference value is not completely obvious if there are observations and/or labs that could be considered outliers.� Since ignoring results from one or more participating laboratories is untenable in practical terms,� developing methods that are robust to the possibility that a small fraction of the labs produce observations unlike those from the others is critical.� This talk outlines two Bayesian methods of analyzing inter-laboratory data that have been proposed in the literature and suggests three modifications of one that are more robust to outliers.� A simulation study is conducted to compare the five methods.