Area under the curve (AUC) summarizes how well a binary classification model distinguishes positive cases from negative cases. It is calculated from the receiver operating characteristic (ROC) curve, which plots specificity against sensitivity. An AUC of 1 represents perfect discrimination, 0.5 represents random chance, and higher values indicate stronger overall discriminatory power. section 14.6.2
Unlike error rate and accuracy, which count individual classifications at a chosen threshold, AUC evaluates the model's overall ability to separate the two classes. Sensitivity and specificity therefore provide complementary information rather than interchangeable results. section 14.6.2
NBA playoff prediction
A logistic regression predicted whether NBA teams qualified for the playoffs. Passing actual outcomes and predictions to pROC's roc() function produced an AUC of 0.73, indicating fairly strong predictive performance. The ROC curve can then be drawn with base R's plot() function. Comparing a second model shows why AUC matters: one model can have higher sensitivity while another has higher specificity, yet their AUCs can be essentially equal. section 14.6.2
Use AUC to:
- Compare binary classification models by overall discriminatory power. section 14.6.2
- Interpret ROC plots alongside sensitivity, specificity, accuracy, and error rate. section 14.6.2











