Figure 1

The two-graph receiver operating characteristics curve, with cut-off values for the blocking ELISA test given as percent inhibition (PI) and ranging from PI 10 to 80 (by increments of 2). Sensitivity (black triangle) and specificity (black dot) for the ELISA were estimated by the use Bayesian modelling techniques. The intersection of the lines corresponds to the cut-off value for the ELISA test recommended by the manufacturer, PI 30. The 95% probability intervals are given by the dotted lines.