Model evaluation validation metrics frameworks

Implement comprehensive model evaluation and validation frameworks with proper metrics and statistical analysis. Classification metrics: 1. Accuracy: correct predictions / total predictions, baseline comparison, stratified sampling. 2. Precision: true positives / (true positives + false positives), minimize false alarms. 3. Recall (Sensitivity): true positives / (true positives + false negatives), capture all positive cases. 4. F1-score: harmonic mean of precision and recall, balanced metric for imbalanced datasets. Regression metrics: 1. Mean Absolute Error (MAE): average absolute differences, interpretable units, robust to outliers. 2. Root Mean Square Error (RMSE): penalizes large errors, same units as target variable. 3. R² (coefficient of determination): explained variance, 1.0 = perfect fit, negative = worse than mean. Advanced evaluation: 1. ROC-AUC: area under ROC curve, threshold-independent, >0.9 excellent performance. 2. Precision-Recall curve: imbalanced datasets, focus on positive class performance. 3. Confusion matrix: detailed error analysis, class-specific performance, misclassification patterns. Cross-validation strategies: 1. Stratified K-fold: maintain class distribution, k=5 or k=10, repeated CV for stability. 2. Time series validation: walk-forward, expanding window, respect temporal dependencies. 3. Leave-one-out: small datasets, computationally expensive, unbiased estimates. Statistical significance: 1. Paired t-test: compare model performance, statistical significance p<0.05. 2. Bootstrap sampling: confidence intervals, performance stability assessment. 3. McNemar's test: classifier comparison, statistical hypothesis testing. Business metrics integration: ROI calculation, cost-benefit analysis, domain-specific targets, A/B testing framework for production validation.