Fig. 2

Plot of the null distribution of 10,000 Fisher’s exact test p-values under the two-phase design with group size 5 from Monte Carlo approach for an antibody prevalence of 0.2. Large column on the right shows those instances that did not advance to phase 2, and therefore are considered not significant. Red vertical line indicates the 5th percentile of all p-values, and therefore the determined phase 2 cutoff that should be used to maintain an overall rejection rate and alpha level of 0.05