The Guide to the Expression of Uncertainty in Measurement - Bayes, doped horses and chemistry


Emeritus Professor D Brynn Hibbert FRSN


School of Chemistry, UNSW


Tue, 02/05/2017 -
11:05am to 11:55am


Rupert Myers Theatre, UNSW


The seminar will be descriptions of an eclectic mix of mathematical and statistical methods applied in chemistry, with the unifying theme that the author has had a hand in each of them.

The Guide to the Expression of Uncertainty in Measurement (1) is published by Working Group 1 of the Joint Committee for Guides on Metrology, a group on which the author represented Chemistry (through IUPAC) from 2007-2015. Last revised in 2008, the committee has been working to prepare an edition for 2017. Evaluation of measurement uncertainty can be complex and is done in a quasi-Bayesian way, but the results are vital for the interpretation of measurement results in trade, health, forensics and the environment. The problem is to maintain rigour while providing methodology that can be used by practitioners.

A current topic of discussion, without any great outcomes, is how to treat the uncertainty of the determination of nominal properties, for example the identification of a drug, which can be seen as occupying a position in a multidimensional space defined by its atoms and their linkages. The analogue drug laws will be discussed and a question will be asked (2).

Analysing chemical data in racing animals is done to obtain regulatory limits of chemicals such as cobalt and carbon dioxide (3) by determining levels at which, for a ‘typical’ animal, the probability is ‘essentially zero’. Tracking drugs of abuse from the analysis of stable isotopes (13C, 2H, 15N) has allowed authorities to track illicit ice manufacture, and curtail the use of testosterone abuse in athletes. Methamphetamine data was classified done using expectation maximisation in a Gaussian mixture model (4).

1. Joint Committee for Guides in Metrology JCGM 100: Evaluation of measurement data - Guide to the expression of uncertainty in measurement; BIPM: Sèvres, 2008.

2. Hibbert, D. B.; Sutton, J., A chemical view of analogue drug laws in Australia. What is structural similarity? Australian Journal of Forensic Sciences 2016, 1 - 21.

3. (a) Hibbert, D.; Armstrong, N.; Vine, J., Total CO2 measurements in horses: where to draw the line. Accred. Qual. Ass. 2011, 16 (7), 339-345; (b) Sutton, G. J.; Cawley, A.; Murphy, C.; Lau, M. L.; Hibbert, D. B., Factors influencing total carbon dioxide concentrations in plasma of thoroughbred and standardbred racehorses. Drug Testing and Analysis 2014, 6 (9), 936-943.

4. Salouros, H.; Sutton, G. J.; Howes, J.; Hibbert, D. B.; Collins, M., Measurement of Stable Isotope Ratios in Methylamphetamine: A Link to Its Precursor Source. Anal. Chem. 2013, 85 (19), 9400-9408.

School Seminar Series: