An optimised uncertainty (OU) methodology is described, that
balances the uncertainty of measurements on food against the cost of the
measurements and the other expenditure that may arise as a consequence of
the possible misclassification of the food. Measurement uncertainty from
the sources of primary sampling and chemical analysis is estimated using an
existing technique, which is based on the taking of duplicated samples and
duplicated analyses. The input information required for the OU method is
the actual costs of sampling and analysis, and the expected costs that
could arise from either the ‘false positive’ or ‘false
negative’ classification of batches of food. A loss function is then
constructed that calculates the ‘expectation of loss’ which
will arise for a given uncertainty of measurement. This function has a
minimum value of cost at an optimal value of uncertainty, which can be
estimated numerically. Application of this OU method to a case study on the
determination of aflatoxin levels in pistachio nuts has demonstrated this
minimum value. Below the optimum value of uncertainty, the costs increased
due to higher measurement costs. Above the optimum value, the costs
increased due to increasing probability of expenditure on consequences such
as unnecessary rejection of the batch, potential litigation or loss of
corporate reputation because of undetected contamination. A second stage of
the OU method optimises the division of the expenditure on the measurement
between that on sampling and that on analysis. The technique is
demonstrated as a useful new approach for judging the fitness-for-purpose
of chemical measurements in the food industry. Several areas for further
development of the technique are identified. By matching the expenditure on
the measurement against that caused by the misclassification of the food,
the OU method has the potential to reduce overall expenditure whilst
ensuring an appropriate reliability of measurement.
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