Model Evaluation Metrics: Model evaluation metrics quantify machine learning performance through mathematical formulations capturing different aspects of predictive quality, from classification accuracy and regression errors to ranking effectiveness and probabilistic calibration. The engineering challenge involves selecting metrics aligned with business objectives, understanding metric relationships and tradeoffs, computing confidence intervals for statistical significance, handling multi-output and hierarchical predictions, and translating technical metrics into stakeholder-interpretable performance indicators. Model Evaluation Metrics explained for People without AI-Background - Model evaluation metrics are like different ways of grading a student's performance - just as you might measure accuracy (test scores), speed (time to complete), consistency (variation across tests), and improvement (progress over time), different metrics reveal different strengths and weaknesses of machine learning models, with the right metric depending on what matters most for your specific problem. Why Do Different Metrics Capture Distinct Performance Aspects? Different metrics emphasize various error types and prediction characteristics, with no single metric fully characterizing model performance necessitating multi-metric evaluation. Accuracy (correct/total) weights all errors equally becoming meaningless with class imbalance - 99% accurate predicting all negative with 1% positive rate. Mean Squared Error penalizes large errors quadratically making it sensitive to outliers, while Mean Absolute Error treats all errors linearly providing robustness. Logarithmic loss evaluates probability quality beyond hard predictions, heavily penalizing confident wrong predictions essential for risk-sensitive applications. Area Under ROC Curve measures discrimination ability independent of threshold, while precision-recall curves better characterize performance on imbalanced datasets. Each metric's mathematical formulation embeds assumptions about error costs and decision contexts.