Answer Happy

1.5 Draw the ideal ROC curve for a device. Can a device have a ROC curve that lies below the dotted line in Figure 1.8? If so, suggest one situation involving a medical device that could produce such a line.

Figure 1.8 Example of a receiver operating characteristic curve (grey dashed line) for a medical instrument. The dotted line represents the performance of an instrument that has no prognostic value. axis corresponds to essentially a random True positive fraction measurement with no prognostic value. The more the ROC curve lies above this line, the better the device. In this way. a new device can be compared with an existing one. Two very commonly quoted parameters for a device are the sensitivity and specificity. The sensitivity of a device is defined as the number of 0.5 1.0 False positive fraction true positives divided by the sum of the true positives and false negatives, and the specificity is the number of true negatives divided by the sum of the number of true negatives and false positives.