Model evaluation is the process of assessing how well a machine learning model performs on unseen data to ensure it generalises rather than just memorising the training set.
Core Validation Techniques
• Holdout Method: Splits the dataset into training and testing sets (commonly 7:3 or 8:2 ratios).
• K-Fold Cross-Validation: Divides data into k subsets; the model trains on k-1 folds and tests on the remaining fold, repeating this process k times to prevent overfitting.
• Temporal Validation: Evaluates models on time-based split data to mimic real-world production performance.
Classification Evaluation Metrics
Classification models assign data to discrete categories.
• Accuracy: The ratio of total correct predictions to all predictions (can be misleading with imbalanced datasets).
• Precision: The proportion of positive predictions that are actually correct (critical when false positives are costly).
• Recall (Sensitivity): The proportion of actual positives correctly identified (critical when false negatives are dangerous, such as disease detection).
• F1 Score: The harmonic mean of precision and recall, balancing both metrics.
• Confusion Matrix: A table (True Positive, True Negative, False Positive, False Negative) showing detailed classification errors.
• AUC-ROC Curve: Measures the area under the Receiver Operating Characteristic curve, showing the model's ability to distinguish between classes across thresholds.
Regression Evaluation Metrics
Regression models predict continuous numerical values.
• Mean Absolute Error (MAE): The average of absolute differences between predicted and actual values.
• Mean Squared Error (MSE): The average of squared differences, heavily penalizing large outliers.
• Root Mean Squared Error (RMSE): The square root of MSE, returning the error to the original target unit.
• R-Squared (R²): Measures the proportion of variance in the dependent variable explained by the model compared to a baseline mean predictor.
Best Practices & Pitfalls
• Avoid Data Leakage: Ensure test data or future metrics never bleed into the training pipeline.
• Match Metrics to Business Goals: Do not rely on raw accuracy alone for skewed data; choose metrics aligned with the cost of false positives vs. false negatives.
• Transition to Monitoring: Shift from pre-deployment model evaluation to continuous post-deployment model monitoring to catch data drift.
https://www.geeksforgeeks.org/machine-learning/machine-learning-model-evaluation/
https://www.ibm.com/think/topics/model-evaluation
https://www.ibm.com/think/topics/model-performance
https://www.snowflake.com/en/artificial-intelligence/machine-learning/model-evaluation/
https://dl.gi.de/bitstreams/9d5b7a50-3901-406f-b9d4-2eb405f5fbcf/download
https://dl.gi.de/server/api/core/bitstreams/9d5b7a50-3901-406f-b9d4-2eb405f5fbcf/content
https://www.kaggle.com/learn-guide/model-evaluation
https://docs.cloud.google.com/bigquery/docs/evaluate-overview
https://developers.google.com/machine-learning/crash-course/classification/accuracy-precision-recall
Videos
https://www.youtube.com/watch?v=LQrOYxCnk4E