Evaluation
ROC AUC
ROC AUC measures ranking quality across classification thresholds using true-positive and false-positive rates.
How it works
It equals the probability that a random positive receives a higher score than a random negative under standard assumptions. It can look optimistic on highly imbalanced problems.
A concrete example
Illustrative: an illustrative ROC curve has AUC 0.87 across all thresholds.
Do not confuse it with PR AUC
ROC uses false-positive rate; PR uses precision and recall and is often more revealing for rare positives.