AUC Score

AUC Score (Area Under the Curve)

The AUC Score refers to the Area Under the Curve and is a popular metric used to evaluate the performance of classification models, especially in binary classification tasks.

Most commonly, AUC represents the area under the ROC Curve (Receiver Operating Characteristic Curve) or under the Precision-Recall Curve (PR Curve).

What is AUC?

AUC measures the ability of a model to distinguish between positive and negative classes. It summarizes the model’s performance across all classification thresholds.

$0\le \text{AUC}\le 1$

An AUC score closer to 1 indicates a better model, while 0.5 suggests the model performs no better than random guessing.

Types of AUC

• ROC AUC – Area under the ROC curve, measuring trade-offs between True Positive Rate (Recall) and False Positive Rate.
• PR AUC – Area under the Precision-Recall curve, focusing on trade-offs between precision and recall, especially useful for imbalanced datasets.

Interpretation

• AUC = 1

Perfect classification. The model ranks all positives higher than negatives.

• AUC = 0.5

Random guessing. The model has no discrimination ability.

• AUC < 0.5

Worse than random. Indicates model predictions may be reversed.

Why Use AUC?

• Provides a threshold-independent measure of model quality.
• Helps compare models regardless of decision threshold.
• Useful in situations where class distribution is imbalanced.
• Summarizes classifier’s ability to rank positive instances higher than negatives.

How to Calculate ROC AUC (Conceptual)

ROC AUC can be interpreted as the probability that a randomly chosen positive instance is ranked higher than a randomly chosen negative instance by the model.

Example

Imagine a cancer detection model that outputs scores for patients. If the model assigns higher scores to patients with cancer than to healthy patients 90% of the time, the ROC AUC = 0.9.

Limitations

• AUC does not reflect the actual predicted probabilities.
• It does not consider the costs of false positives and false negatives.
• For heavily imbalanced data, Precision-Recall AUC may be more informative.

Related Pages

• ROC Curve
• Precision-Recall Curve
• Model Evaluation Metrics
• Confusion Matrix
• F1 Score
• Precision
• Recall

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