When evaluating a classification model, one of the most commonly used metrics is ROC AUC (Receiver Operating Characteristic – Area Under the Curve). This metric measures how well a model distinguishes between positive and negative classes. However, many data scientists and machine learning practitioners ask the question: What is a good ROC AUC score?
In this article, we will explore:
- The meaning of ROC AUC and how it is calculated
- How to interpret ROC AUC scores
- What constitutes a good ROC AUC score
- The limitations of ROC AUC and when to use alternative metrics
Understanding ROC AUC
What Is ROC AUC?
ROC AUC (Receiver Operating Characteristic – Area Under the Curve) is a metric that evaluates the ability of a classification model to distinguish between classes across different classification thresholds.
The ROC curve plots:
- True Positive Rate (TPR) or Sensitivity (y-axis):
- False Positive Rate (FPR) (x-axis):
The AUC (Area Under the Curve) represents the probability that the classifier ranks a randomly chosen positive instance higher than a randomly chosen negative instance. The higher the AUC, the better the model’s performance in distinguishing between positive and negative classes.
How to Interpret ROC AUC Scores
The ROC AUC score ranges from 0 to 1, where:
- 1.0 (100%) – Perfect classification (ideal model).
- 0.9 – 1.0 (90-100%) – Excellent classification.
- 0.8 – 0.9 (80-90%) – Good classification.
- 0.7 – 0.8 (70-80%) – Fair classification.
- 0.6 – 0.7 (60-70%) – Poor classification.
- 0.5 (50%) – No discrimination (random guessing).
- < 0.5 – Worse than random (model is making incorrect predictions systematically).
Threshold for a Good ROC AUC Score
- ROC AUC > 0.90: The model has high predictive power and performs well.
- ROC AUC between 0.80 and 0.90: The model is good but may need further improvements.
- ROC AUC between 0.70 and 0.80: The model is acceptable, but there is room for enhancement.
- ROC AUC below 0.70: The model is not reliable and may need significant adjustments.
However, a good ROC AUC score depends on the specific application and the balance between precision and recall.
What Is a Good ROC AUC Score in Different Applications?
When evaluating a classification model, the definition of a “good” ROC AUC score varies depending on the application. Different industries and use cases have distinct requirements for model performance, and what is considered acceptable in one field may be insufficient in another.
1. Medical Diagnosis
- Example: Predicting whether a patient has cancer, heart disease, or another critical condition.
- Good ROC AUC Score: 0.90+
- Why? In healthcare, false negatives can have severe consequences, such as missing a cancer diagnosis. High sensitivity (recall) is crucial to ensuring as many positive cases as possible are correctly identified. A model with an ROC AUC below 0.85 may not be reliable for clinical use.
2. Fraud Detection
- Example: Identifying fraudulent credit card transactions or insurance claims.
- Good ROC AUC Score: 0.85+
- Why? Fraudulent cases are rare compared to legitimate ones, making fraud detection an imbalanced classification problem. Since false positives (flagging a legitimate transaction as fraud) can inconvenience customers, while false negatives (missing fraud) can cause financial losses, a balance between precision and recall is essential. A ROC AUC above 0.85 is typically required for practical fraud detection systems.
3. Spam Detection
- Example: Classifying emails as spam or not spam.
- Good ROC AUC Score: 0.80+
- Why? Spam filtering involves a trade-off: flagging too many emails as spam can cause users to miss important messages (false positives), while missing spam emails can result in unwanted messages in the inbox (false negatives). A ROC AUC above 0.80 is generally acceptable, but many modern spam filters aim for 0.90+.
4. Customer Churn Prediction
- Example: Predicting whether a customer will stop using a subscription service or product.
- Good ROC AUC Score: 0.75+
- Why? While customer churn is an important business metric, a moderate ROC AUC score (above 0.75) may be acceptable, as businesses can also rely on alternative retention strategies. Models for churn prediction prioritize practical use, so precision and recall may be more critical than optimizing the highest possible ROC AUC.
5. Credit Risk Modeling
- Example: Predicting whether a loan applicant will default on a loan.
- Good ROC AUC Score: 0.80 – 0.90
- Why? Banks and financial institutions use credit risk models to assess borrower risk. A high ROC AUC score is necessary to ensure responsible lending practices. A score below 0.75 may lead to high-risk loans being approved, while a score above 0.90 is ideal but challenging to achieve due to real-world financial complexities.
6. Image Recognition (Binary Classification Tasks)
- Example: Detecting whether an image contains a specific object, such as identifying tumors in medical imaging.
- Good ROC AUC Score: 0.90+
- Why? In high-stakes applications like medical imaging or security surveillance, precision is critical. A model needs to accurately distinguish between positive and negative cases, ensuring minimal false negatives.
7. Sentiment Analysis
- Example: Classifying customer reviews as positive or negative.
- Good ROC AUC Score: 0.75+
- Why? Sentiment analysis models are often used in marketing and customer service. While accuracy is valuable, some level of misclassification is tolerable, making a ROC AUC score above 0.75 generally acceptable.
Limitations of ROC AUC
1. Not Reliable for Imbalanced Datasets
If the dataset has a significant class imbalance (e.g., fraud detection where fraud cases are rare), ROC AUC can be misleading. A model may have a high ROC AUC score but still fail at predicting positive cases.
Solution: Use PR AUC (Precision-Recall AUC) instead, as it focuses on the positive class.
2. Does Not Consider Decision Thresholds
ROC AUC evaluates model performance across all classification thresholds, but real-world applications require a specific threshold for decision-making.
Solution: Use F1-score or Precision-Recall trade-offs for setting optimal thresholds.
3. Can Be Inflated by Overfitting
A very high ROC AUC score (close to 1.0) might indicate overfitting if the model has been excessively trained on the dataset.
Solution: Use cross-validation to check if the model generalizes well to new data.
Alternative Metrics to Consider
If ROC AUC is not the best fit, consider alternative evaluation metrics:
| Metric | When to Use |
|---|---|
| PR AUC (Precision-Recall AUC) | For imbalanced datasets where detecting positive cases is more important. |
| F1-Score | When precision and recall need to be balanced. |
| Accuracy | When the dataset is balanced and both classes are equally important. |
| Matthews Correlation Coefficient (MCC) | For evaluating binary classification with imbalanced data. |
Conclusion
A good ROC AUC score depends on the problem domain and the model’s intended use.
✔ For high-stakes applications (e.g., medical diagnosis, fraud detection): Aim for 0.85+. ✔ For general classification tasks (e.g., spam detection, customer churn): A score above 0.75+ is reasonable. ✔ For imbalanced datasets: Consider using PR AUC instead of ROC AUC.
While ROC AUC is a powerful metric, it should not be the sole criterion for evaluating model performance. Instead, use it alongside precision, recall, F1-score, and domain-specific requirements to make informed decisions about your model’s effectiveness.
By understanding what is a good ROC AUC score, you can improve your model selection and optimize its real-world impact!