4.3 Online tool for calibration of CAD in a new setting

The CAD for TB detection calibration tool has been developed for analysis of the data collected in the CAD calibration protocol described above. The tool estimates the primary outcomes of yield and cost at every possible CAD threshold, including yields of true-positive, true-negative, false-positive and false-negative results; sensitivity and specificity; negative and positive predictive values; proportions of prevalent TB cases diagnosed and missed; and cost implications, including total costs for diagnostic evaluation and cost per true case detected. These values are then used to construct a ROC curve to illustrate the sensitivity and specificity of CAD at a range of possible thresholds. These outputs allow users to visualize potential scenarios and to select a threshold score for a given CAD implementation according to the objectives of the screening programme, the desired accuracy and yield, and the cost implications. The tool also allows users to conduct sub-population analyses for specific patient characteristics, such as separate ROC curves and threshold calculations for individuals who are HIVpositive or who are over 55 years of age. The tool can be found online at https://tdr.who.int/activities/calibrating-computer-aided-detection-for-tb.

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