Figure 2.

Change in positive predictive value by varying sensitivity (A) or specificity (B). Figures show relationship between positive predictive value (% of individuals with tuberculosis [TB] diagnosis that actually have TB disease) and prevalence of disease in screening population for combinations of sensitivity and specificity. A, Lines show how relationship changes if specificity for algorithm 1 (see Table 1) remains constant at 97% but sensitivity increases. B, Lines show how relationship changes if sensitivity remains constant at 53% but specificity increases or decreases.