Analysis of a Random Forests Model

Random forests are a scheme proposed by Leo Breiman in the 2000’s for building a predictor ensemble with a set of decision trees that grow in randomly selected subspaces of data. Despite growing interest and practical use, there has been little exploration of the statistical properties of random forests, and little is known about the mathematical forces driving the algorithm. In this paper, we offer an in-depth analysis of a random forests model suggested by Breiman in [12], which is very close to the original algorithm. We show in particular that the procedure is consistent and adapts to sparsity, in the sense that its rate of convergence depends only on the number of strong features and not on how many noise variables are present. Index Terms — Random forests, randomization, sparsity, dimension reduction, consistency, rate of convergence. 2010 Mathematics Subject Classification: 62G05, 62G20. Research partially supported by the French National Research Agency under grant ANR-09-BLAN-0051-02 “CLARA”. Research carried out within the INRIA project “CLASSIC” hosted by Ecole Normale Supérieure and CNRS. 1 ar X iv :1 00 5. 02 08 v3 [ st at .M L ] 2 6 M ar 2 01 2