The Summary section in the Partition report provides fit statistics for the training data and validation and test data (if used). The fit statistics in the Summary Panel update as you add splits or prune the decision tree.
RSquare
The current value of R2.
N
The number of observations.
Number of Splits
The current number of splits in the decision tree.
RASE
(Available only for continuous responses.) The root average square error. See “RASE” in Fitting Linear Models.
AICc
(Available only for continuous responses.) The corrected Akaike’s Information Criterion. See “Likelihood, AICc, and BIC” in Fitting Linear Models.