SAS EM decision tree purity

[jwoods]

Hi,

I have experience in SAS but I'm having trouble using SAS EM. I have a few questions:

1. How is purity measured/ranked?

2. Is the purity of a node based on the training data or the validation data? 

3. Why is the purity of a node indicated by training/validation (answer to number 2) data?

4. How do you know (by looking at a tree), which nodes are the purist?

Thanks

[WendyCzika]

You can use Gini impurity as the splitting criterion when growing the decision tree, which has formula: