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Using Ruggedness Tests to Estimate Uncertainty


In this study ruggedness tests, suitably designed by a panel of four experts, are applied to ten different chemical analyses. The tests selected are on a range of constituents of foodstuffs (trace elements, trace organic compounds, anions, proximate analytes), covering a concentration range from low traces to major component (89ppb to 56%) and with a variety of chemical and physical principles underlying the procedure. The methods used were selected on the basis of there being a number of published collaborative trials to provide comparison data. All tests being executed by scientists experienced in the methodologies being used.
Critical features of each analytical method are considered and determined in advance by the panel of experts, with the perturbations in the method features being determined by consideration of the uncontrolled variation thought likely to occur between laboratories. However, no factors are considered in the experimental design to accommodate excursions from the written procedure, other than those determined in the design of the ruggedness experiment. The combination of perturbed levels for each complete analysis are to be determined at random, and 20 such complete analyses undertaken for each method on a homogenised laboratory sample of the relevant test material.
After piloting the test on an analytical technique, and a review of the initial design, the modified ruggedness test to will be applied to four more analytical methods in the food sector. After further adjustments to the design, tests will be carried out on the remaining five methods, to compare the uncertainty estimate from the ruggedness tests with estimated as reproducibility precision in the collaborative trial.

More information

Chemical measurements, such as the concentration of a contaminant in a food, underlie most decisions about whether a particular foodstuff is fit to eat. All measurements, including chemical measurements, contain 'uncertainty', a term that indicates the range in which we believe the true result to lie with a high probability. The uncertainty associated with a result is an essential aid to making decisions based on the result gained.
The collaborative trial is one means of providing a benchmark uncertainty for the result of a chemical measurement. However, these trials involve work by a large number of laboratories and are therefore expensive, typically costing about £30,000 per analytical method. The 'ruggedness test' is another possible approach to estimating uncertainty. It is carried out in one laboratory, and therefore much cheaper.
Analytical methods comprise a list of instructions for the chemical operations needed to make the measurement, rather like a recipe. In a ruggedness test, small variations are deliberately introduced into the recipe to see how it affects the outcome. In a good, or 'rugged' method, the measurement result is unaffected by these minor variations. The idea underlying this research is that by making the variations to the recipe appropriately larger, it would be possible to simulate the degree of variation that would be observed in a collaborative trial. However, the standard ruggedness test is only regarded as a screening test and incapable of providing good estimates of uncertainty.
The aim of the research was to determine whether a standard ruggedness test could be modified in such a way as to provide data with the same validity as a collaborative trial but at a much smaller cost.
Find more about this project and other FSA food safety-related projects at the <a href="; target="_blank">Food

Standards Agency Research webpage</a>.

Birkbeck College
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