Decision Trees tutorial > Exercise 6:

Pruning

The dataset:

The Holdout (validation) data

Select rows by clicking to move data instances (rows) between tables

The Decision Tree: Interactively build it

• Click on the root node below and start building the tree.
• Non leaf nodes can be "pruned" once they have been chosen (by clicking on the node and selecting "prune node completely")
• The ratios on the branches indicate how well the chosen attribute at a node splits the remaining data based on the target attribute ('outcome').
• Click on any nodes to hilight the rows in the data table that the rule down to that node covers.
• At each node, the entropy of the data at that point in the tree will be given.
• Information gain (entropy reduction) is specified for each attribute.
• Reducing entropy to zero is a way of building a decision tree here. When no more nodes can be expanded, the tree has classified all the training data.
• Move data into the testing set from the training set (by clicking) and then contsruct a tree. Ideally a testing set should have 33% or less of the training data (about 3 or 4 instances here).
• Prune branches by replacing them with a single leaf node in order to improve combined classification accuracy.

Classification Errors (Totals)