Effect of uncertainty in the accuracy of screening and diagnostic tests and assumptions about clinical diagnosis on the NNS and PPV, assuming 1% TB prevalence in the screened population. Panel A: Variation in the number needed to screen (NNS); Panel B: Variation in the positive predictive value (PPV). The symbols represent the point estimates and the vertical bars the range due to uncertainty in the model parameter, as specified in Table 2. The specific scenarios are listed in Table 3. CXR = chest X-ray for screening; SSM = sputum smear microscopy; XP = Xpert MTB/RIF; 1 = first screen; 2 = second screen if first is positive. SSA = sub Saharan Africa.