The evaluation of bias in scrapie surveillance: a review

Evaluation of surveillance systems is a common practice in the context of human health, but only recently has been applied in the veterinary field. Commonly, a series of attributes are monitored to assess the system. Suboptimal performance of the surveillance in relation to any of these attributes may lead to bias in the surveillance results. The intensity of scrapie surveillance has increased considerably in recent years as a result of public health concerns. In this paper, a number of approaches described in the literature for the evaluation of surveillance systems are reviewed, with a focus on the sensitivity and representativeness attributes of scrapie surveillance systems in the European Union. Many of the methods applied in other fields, such as ecology and public health, are exchangeable and relevant for scrapie surveillance.