E=0 E=1   X=0 M(1-t) fx0 (NPV) M(1-t) fx0 (1-NPV)  M(1-t) fx0  Mt fx1 N X=1 Mt fx1(1-PPV) Mt fx1(PPV)   N0 N1 M Total sample size of the Stage I study τ Probability of a positive screening test = Pr[X=1] fx0 Sampling fraction of those testing negative from the screening test at Stage I fx1 Sampling fraction of those testing positive from the screening test at Stage I N Total sample size of the Stage II study with N0 and N1 in the non-exposure group and the exposure group, respectively

Table 3: Expected Cell Counts of the Exposure (E) cross-classified by Screening Test (X)