Overfitting, Underfitting and Model Selection
This passage discusses the concept of model selection in polynomial regression, focusing on determining the appropriate order of the polynomial to avoid underfitting and overfitting.
Underfitting and Overfitting: It explains the concepts of underfitting and overfitting in polynomial regression. Underfitting occurs when the model is too simple to fit the data, resulting in high errors. Overfitting happens when the model is too flexible and fits the noise rather than the underlying function, leading to poor generalization performance.
Model Complexity and Mean Square Error: The passage illustrates how the mean square error changes with the order of the polynomial. It shows that the training error decreases with increasing polynomial order, but the test error provides a better estimate of the model's performance. The test error initially decreases as the polynomial order increases, reaches a minimum, and then starts to increase, indicating the optimal polynomial order.
Irreducible Error and Other Sources of Error: It mentions the presence of irreducible error, which arises from the random noise in the data that cannot be predicted. Additionally, other sources of errors, such as incorrect assumptions about the polynomial function or data generation process, are discussed.
Selecting the Optimal Polynomial Order: The passage demonstrates how to select the optimal polynomial order using the R^2 value, which measures the goodness of fit of the model. It suggests choosing the polynomial order that maximizes the R^2 value on the test data. An example code snippet is provided to calculate R^2 values for different polynomial orders using a loop and polynomial feature transformation.
Overall, the passage highlights the importance of selecting the appropriate polynomial order to balance between underfitting and overfitting, and it provides insights into using the test error and R^2 value for model selection in polynomial regression
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