Fig 2. The theoretical fraction of random animals required to be tested from finite sheep flock (n = 200) in order to demonstrate that the population is SBV infected.

Calculations with sensitivities and specificities (Se/Sp) obtained from total control testing from two scenarios: (A) all suspect/doubtful reads were included in positive results, (B) all suspect/doubtful reads were included in negative results. The results for the given theoretical prevalence are shown for Serum Neutralisation Test (SNT), ID.Vet test and IDEXX test. A minimum number of positive animals needed to be recognised from all tested animals in order to conclude that the population is SBV infected is indicated in square brackets for each test. NA—an error if the calculations could not be achieved within the limits of the population and/or maximum sample size.