Mastering Machine Learning with R - Second Edition

Classification trees

Classification trees operate under the same principle as regression trees, except that the splits are not determined by the RSS but an error rate. The error rate used is not what you would expect where the calculation is simply the misclassified observations divided by the total observations. As it turns out, when it comes to tree-splitting, a misclassification rate, by itself, may lead to a situation where you can gain information with a further split but not improve the misclassification rate. Let's look at an example.

Suppose we have a node, let's call it N0, where you have seven observations labeled No and three observations labeled Yes, and we can say that the misclassified rate is 30 percent. With this in mind, ...