Look at data to evaluate uncertainty. A comment on 'Uranium assay determination' by Mathew et al

In a recent paper, Mathew et al. detailed, for a specific titration-based assay of uranium, a 'step-by-step approach to calculate the GUM uncertainty of the measurand', in which their uncertainty assessment was based solely on prior knowledge, ignoring the manifest variability in their replication data. A simple analysis of the variance from their data reveals that the uncertainty in the average of the replicated quantity (TEF) was at least 3.5 times their estimate. Since the observables that contribute most to the final uncertainty in their method were not replicated, it is unknown whether the estimates for the uncertainties of those quantities, and thus of the output quantity, were also underestimated. This comment demonstrates how a better uncertainty evaluation is possible by extracting as much knowledge as possible from the extant data. (author)