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Questions and Answers
The test set is used to select the final model.
The test set is used to select the final model.
False (B)
Hyperparameters are learned from the training data.
Hyperparameters are learned from the training data.
False (B)
Accuracy is the only metric used to evaluate a classification model.
Accuracy is the only metric used to evaluate a classification model.
False (B)
The confusion matrix is used to evaluate regression models.
The confusion matrix is used to evaluate regression models.
The validation set is used to evaluate the model's performance on unseen data.
The validation set is used to evaluate the model's performance on unseen data.
True Positives are when you predict negative and it's true.
True Positives are when you predict negative and it's true.
False Negatives are when you predict positive and it's false.
False Negatives are when you predict positive and it's false.
Precision is a metric used to evaluate regression models.
Precision is a metric used to evaluate regression models.
The accuracy of the model can be calculated from the given confusion matrix.
The accuracy of the model can be calculated from the given confusion matrix.
The sensitivity of a classifier is the ratio of correctly predicted negative observations to all actual negative observations.
The sensitivity of a classifier is the ratio of correctly predicted negative observations to all actual negative observations.
The F-score is a measure of precision only.
The F-score is a measure of precision only.
The holdout method is a type of cross-validation.
The holdout method is a type of cross-validation.
Cross-validation is a method for training a model.
Cross-validation is a method for training a model.
The precision of a classifier is the ratio of true positives to all positive predictions.
The precision of a classifier is the ratio of true positives to all positive predictions.
Bootstrap is a method for constructing a training set and testing set from the original dataset.
Bootstrap is a method for constructing a training set and testing set from the original dataset.
The error rate of a model is the same as its accuracy.
The error rate of a model is the same as its accuracy.
The training set is used to evaluate the function approximator's performance.
The training set is used to evaluate the function approximator's performance.
K-Fold Cross Validation is a method that eliminates selection bias.
K-Fold Cross Validation is a method that eliminates selection bias.
In Leave-one-out Cross Validation, the training set is always larger than the testing set.
In Leave-one-out Cross Validation, the training set is always larger than the testing set.
Bootstrap is a resampling technique without replacement.
Bootstrap is a resampling technique without replacement.
The average error rate on the test set is used to estimate the true error in K-Fold Cross Validation.
The average error rate on the test set is used to estimate the true error in K-Fold Cross Validation.
Leave-one-out Cross Validation is a computationally efficient method.
Leave-one-out Cross Validation is a computationally efficient method.
K-Fold Cross Validation is a method that ensures the training set is always the same size.
K-Fold Cross Validation is a method that ensures the training set is always the same size.
Bootstrap is a method used to evaluate the performance of a classifier.
Bootstrap is a method used to evaluate the performance of a classifier.
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Study Notes
Data Sets
- Train, Validation (Dev), and Test Sets are used in the workflow of training and evaluating a model
- Train set: used to train the model
- Validation set: used to select the best model from many trained models
- Test set: used to evaluate the final model on unseen data
Mismatch
- Dev and Test sets should come from the same distribution
Metrics for Evaluating Classifier Performance
- Evaluation metrics quantify the performance of a machine learning model
- Accuracy: percentage of correct classifications
- Calculation: (correct predictions / total predictions) * 100
- Example: actual outputs = [0,0,1,1,0,0,0,1,0,1,1,0], predicted outputs = [0,1,1,0,1,0,0,1,0,1,1,1]
Confusion Matrix
- A table that describes the performance of a classification model
- Elements:
- True Positive (TP): predicted positive and true
- True Negative (TN): predicted negative and true
- False Positive (FP): predicted positive and false
- False Negative (FN): predicted negative and false
Sensitivity and Specificity
- Sensitivity (Recall or True Positive Rate): ratio of correctly predicted positive observations to all actual positive observations
- Calculation: TP / (TP + FN)
- Specificity (True Negative Rate): ratio of correctly predicted negative observations to all actual negative observations
- Calculation: TN / (TN + FP)
Precision and F-score
- Precision: fraction of relevant examples (true positives) among predicted positives
- Calculation: TP / (TP + FP)
- F-score (F1 score): balances precision and recall in one number
- Calculation: 2 * (precision * recall) / (precision + recall)
Model Evaluation Methods
- Goal: choose a model with the smallest generalization error
- Methods to construct training and testing sets:
- Holdout
- Leave-one-out Cross Validation
- Cross Validation (K-Fold)
- Bootstrap
Holdout Method
- Simplest kind of cross-validation
- Divide dataset into two sets: training set and testing set
- Train model on training set and evaluate on testing set
Cross Validation: K-Fold
- Divide dataset into k subsets
- Repeat holdout method k times, using each subset as the test set and the other subsets as the training set
- Calculate average error across all trials
Leave-one-out Cross Validation
- Use n-1 examples for training and the remaining example for testing
- Repeat this process n times, calculating the average error rate on the test set
- Disadvantage: computationally expensive
Bootstrap
- Resampling technique with replacement
- Randomly select examples from the dataset with replacement
- Use selected examples for training and the remaining examples for testing
- Repeat this process for a specified number of folds (k)
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