Visualizing PerformanceWhat Makes A Good ROC Curve?
The shape of an ROC curve shows how well the scores separate the two groups. Here is a smaller test with 8 patients and 8 healthy people. Drag the patients' scores left or right and complete the missions.
When the two groups get the same scores, every threshold catches patients and healthy people at the same rate, and the curve is the diagonal — no better than tossing a coin. When every patient outscores every healthy person, one threshold catches them all with no false alarm, and the curve runs up the left edge to the top-left corner. Real tests sit in between: the more the curve bulges towards the top-left, the better the test.
Name the Curves
Three tests, three curves.
Curve A belongs to
Beware of perfection
Real tests are almost never perfect. If a model's curve hugs the top-left corner on the very first try, suspect a data leak — some information about the answers sneaked into the training data — before you celebrate.