Can ROC curve below diagonal?
The ROC curve (purple curve) could always be below the diagonal. Ie for all threshold values its performance is worse than random. Alternatively the ROC curve may cross the diagonal.
What does the diagonal line on the ROC curve represent?
The diagonal line in a ROC curve represents perfect chance. In other words, a test that follows the diagonal has no better odds of detecting something than a random flip of a coin. The area under the diagonal is . 5 (half of the area of the graph).
What does the area under an ROC curve represent?
As the area under an ROC curve is a measure of the usefulness of a test in general, where a greater area means a more useful test, the areas under ROC curves are used to compare the usefulness of tests. The term ROC stands for Receiver Operating Characteristic.
What do the points on a ROC curve mean?
The ROC curve shows the trade-off between sensitivity (or TPR) and specificity (1 – FPR). Classifiers that give curves closer to the top-left corner indicate a better performance. As a baseline, a random classifier is expected to give points lying along the diagonal (FPR = TPR).
How does a discrete classifier create a ROC curve?
A discrete classifier that returns only the predicted class gives a single point on the ROC space. But for probabilistic classifiers, which give a probability or score that reflects the degree to which an instance belongs to one class rather than another, we can create a curve by varying the threshold for the score.
How are ROC curves used in Clinical Biochemistry?
ROC curves are used in clinical biochemistry to choose the most appropriate cut-off for a test. The best cut-off has the highest true positive rate together with the lowest false positive rate.
Which is the correct ROC curve for perfect discrimination?
A test with perfect discrimination (no overlap in the two distributions) has a ROC curve that passes through the upper left corner (100% sensitivity, 100% specificity). Therefore the closer the ROC curve is to the upper left corner, the higher the overall accuracy of the test (Zweig & Campbell, 1993).