Figure 3

Comparative sample size of serological surveys derived from the pre-SPF. Comparative sample sizes for the follow-up survey derived from the model output pre-survey probability of infection freedom (pre-SPF). Standard sample sizes (SSS), risk-based sample sizes (RBS), with or without detection of newly infected herds, were used to define the herd prevalence (HP) of the previous survey. Ninety-five percent confidence intervals of pre-survey probability of infection freedom and hence resulting sample sizes, were obtained by exact binomial confidence intervals based on the proportion of iterations with values < 0.2 and < 0.1%, respectively, to the total number of iterations performed. Sample sizes were calculated with Survey Toolbox^® assuming a population of 50,000 herds, 99% herd sensitivity for diagnostic testing and a threshold HP of 0.2% and 0.1%, respectively.