Summary

In this chapter, we've learned how to use decision trees and the ensemble models called random forests that are made up of many decision trees. Using these simply conceived models, we were able to make better predictions than we could with logistic regression, judging by the cross-validation ROC AUC score. This is often the case for many real-world problems. Decision trees are robust to a lot of the potential issues that can prevent logistic regression models from good performance, such as non-linear relationships between features and the response variable, and the presence of complicated interactions among features.

Although a single decision tree is prone to overfitting, the random forest ensemble method has been shown to reduce this high-variance issue. Random forests are built by training many trees. The decreased variance of the ensemble of trees is achieved by increasing the bias of the individual trees in the forest, by only training them on a portion of the...