An Experimental Study on Rotation Forest Ensembles

Rotation Forest is a recently proposed method for building classifier ensembles using independently trained decision trees. It was found to be more accurate than bagging, AdaBoost and Random Forest ensembles across a collection of benchmark data sets. This paper carries out a lesion study on Rotation Forest in order to find out which of the parameters and the randomization heuristics are responsible for the good performance. Contrary to common intuition, the features extracted through PCA gave the best results compared to those extracted through non-parametric discriminant analysis (NDA) or random projections. The only ensemble method whose accuracy was statistically indistinguishable from that of Rotation Forest was LogitBoost although it gave slightly inferior results on 20 out of the 32 benchmark data sets. It appeared that the main factor for the success of Rotation Forest is that the transformation matrix employed to calculate the (linear) extracted features is sparse.