Pruning Trees

With the CRT and QUEST methods, you can avoid overfitting the model by pruning the tree: the tree is grown until stopping criteria are met, and then it is trimmed automatically to the smallest subtree based on the specified maximum difference in risk. The risk value is expressed in standard errors. The default is 1. The value must be non-negative. To obtain the subtree with the minimum risk, specify 0.

To Prune a Tree

This feature requires the Decision Trees option.

1. From the menus choose:

   Analyze > Classify > Tree...

2. In the main Decision Tree dialog box, for the growing method, select CRT or QUEST.
3. Click Criteria.
4. Click the Pruning tab.

Pruning versus Hiding Nodes

When you create a pruned tree, any nodes pruned from the tree are not available in the final tree. You can interactively hide and show selected child nodes in the final tree, but you cannot show nodes that were pruned in the tree creation process. See the topic Tree Editor for more information.