pixel acc 、mean acc、 IU、 FWIU (pixel accuracy 、mean accuraccy 、mean IU 、frequency weighted IU)

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### Mean Decrease Accuracy in Machine Learning Explained In machine learning, particularly within the context of feature importance evaluation for tree-based models like Random Forests, **Mean Decrease Accuracy** serves as a critical metric. This measure evaluates how much removing or permuting the values of each predictor variable decreases the accuracy of predictions made by the model. When calculating this metric, the process involves measuring the decrease in prediction accuracy when out-of-bag observations are used on which to calculate an error rate after randomly permuting columns one at a time[^3]. The larger the drop in accuracy due to permutation, the more important that particular feature is considered to be for accurate predictions. For instance, consider a dataset where features significantly contribute to predicting outcomes accurately. If shuffling a specific feature's data points leads to a substantial reduction in overall predictive performance, it indicates high significance of that feature towards achieving correct classifications or regressions. This method provides insights into understanding not only individual contributions but also interactions between different variables impacting final results produced by ensemble methods such as those employing bagging techniques. ```python from sklearn.datasets import load_iris from sklearn.model_selection import train_test_split from sklearn.ensemble import RandomForestClassifier import numpy as np # Load Iris Dataset data = load_iris() X_train, X_test, y_train, y_test = train_test_split(data.data, data.target, test_size=0.2) # Train Model model = RandomForestClassifier(n_estimators=100) model.fit(X_train, y_train) # Calculate Feature Importances using Mean Decrease Accuracy baseline_accuracy = model.score(X_test, y_test) feature_importance_scores = [] for i in range(X_test.shape[1]): temp_data = X_test.copy() np.random.shuffle(temp_data[:,i]) shuffled_accuracy = model.score(temp_data, y_test) decrease_in_accuracy = baseline_accuracy - shuffled_accuracy feature_importance_scores.append(decrease_in_accuracy) print(feature_importance_scores) ```
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