This node draws ROC curves for two-class classification problems. The input table
must contain a column with the real class values (including all class values as possible values)
and a second column with the probabilities that an item (=row) will be classified as being
from the selected class. Therefore only learners/predictors that output class probabilities can
In order to create a ROC curve for a model, the input table is first sorted by the class probabilities for the positive class i.e. rows for which the model is certain that it belongs to the positive class are sorted to front. Then the sorted rows are checked if the real class value is the actually the positive class. If so, the ROC curve goes up one step, if not it goes one step to the right. Ideally, all positive rows are sorted to front, so you have a line going up to 100% first and then going straight to right. As a rule of thumb, the greater the area under the curve, the better is the model.
You may compare the ROC curves of several trained models by first joining the class probability columns from the different predictors into one table and then selecting several column in the column filter panel.
The light gray diagonal line in the diagram is the random line which is the worst possible performance a model can achieve.
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