Figure 4From: Choosing algorithms for TB screening: a modelling study to compare yield, predictive value and diagnostic burden Number needed to screen to find one true case of active TB and positive predictive value of each algorithm at different levels of TB prevalence. Panel A: Number needed to screen (NNS) to find one true positive (TP) case; Panel B: Positive predictive value (PPV). CXR = chest X-ray for screening; SSM = sputum smear microscopy; XP = Xpert MTB/RIF; 1 = first screen; 2 = second screen if first is positive.Back to article page