ROC curves -----------
The diagnosis of a disease is based on a set of criteria. The physician may also call on a battery of tests to support it. A test rarely leads to a certain conclusion; it may prove positive in a healthy patient and negative in someone affected by the disease. It is therefore essential to know a test's ability to discriminate between the population of patients with the disease and that of healthy individuals. This is the purpose of the ROC curve, an acronym for the English term Receiver Operating Characteristic, which was used during the Second World War to distinguish background sea noise from the signal produced by the presence of an enemy submarine.
A given test yields a measurement that is compared with a threshold. For every value of the threshold, the ROC curve is obtained by plotting on the y-axis the rate of "true positives" (the fraction of positives actually detected) and on the x-axis the rate of "false positives" (the fraction of negatives wrongly classified).
-