Qualitative import risk assessment : a proposed method for estimating the aggregated probability of entry of infection

Kelly, L. and Kosmider, R. and Gale, P. and Snary, E. L. (2018) Qualitative import risk assessment : a proposed method for estimating the aggregated probability of entry of infection. Microbial Risk Analysis, 9. pp. 33-37. ISSN 2352-3522

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    In the absence of sufficient numerical data, qualitative risk assessment is recognised as an important tool for providing risk managers with evidence-based predictions on which to formulate their decisions. Such approaches have been used in the area of animal health for import risk assessment for both livestock and zoonotic pathogens. Very few qualitative import risk assessments have, however, considered the aggregated probability of introduction, that is, the probability of at least one infected/contaminated entry per group of import units. Those that have are generally based on specific cases and do not follow a generic approach. In this paper, we consider whether or not it is feasible to develop a generic method and under what circumstances such an approach could be applied in practice. Our conclusion is that it would be difficult to specify a generic method because any such approach would rely on specifying numerical bounds for qualitative categories of probability as well as an idea of the number of imports and would thus be case-specific. As an alternative we propose a way of using case by case information to create a simple graphical reference tool which removes some of the subjectivity that is often associated with deriving qualitative risk. The reference tool considers various qualitative categories of individual probability and determines the relationship between this probability, the number of imports and the aggregated probability of entry. Applying the reference tool to a previously published case-study demonstrated some differences in conclusions and suggests that more subjective approaches can under-estimate probability and thus risk. It is concluded that this approach may be useful for future qualitative assessments of aggregated probability, provided that bounds for qualitative probabilities can be defined for the specific case situation.