title: Comment on 'Empirical versus modelling approaches to the estimation of measurement uncertainty caused by primary sampling' by J. A. Lyn, M. H. Ramsey, A. P. Damant and R. Wood.
abstract: Recently, Lyn et al. (Analyst, 2007, 132, 1231) compared two ways of estimating the standard uncertainty of sampling pistachio nuts for aflatoxins--a modelling method and an empirical method. Their case study used robust analysis of variance (RANOVA) to derive the uncertainty estimates, highlighting a substantial difference between the two: the estimate of sampling uncertainty derived from the modelling method was six-fold greater than that using the empirical approach (cf. 136% and 22.5%, respectively, when expressed as relative standard deviations (RSDs) at 68% confidence). A further analysis of this case study is reported here and suggests that the estimation uncertainty during RANOVA in the empirical approach could account for this difference.
authors.affiliation: Delft University of Technology, Mekelweg 15, 2629 JB, Delft, The Netherlands. B.Geelhoed@tudelft.nl
authors.forename: B
authors.initials: B
authors.lastname: Geelhoed