What is the COMBINE (Bagging, ARCing) Command?
A15. The COMBINE command allows one to choose from several ways of combining separate CART trees into a single predictive engine. The trees are combined by either averaging their outputs for regression or by using an unweighted plurality voting scheme for classification. The current version of CART offers two combination methods: Bootstrap aggregation and ARCing. Each generates a set of trees by resampling (with replacement) from the original training data. When training data are resampled with replacement the effect is to create a new version of the data that is a slightly “perturbed” version of the original. Some original training cases are excluded from the new training sample, and other cases are included multiple times. Typically, 37% of the original cases are not included at all in the resample; the sample is brought up to full size by including other cases more than once. A handful of cases will be replicated 4, 5, 6, or even 7 times, although the most common replication counts
