Variable Selection Bias in Classification Trees Based on Imprecise Probabilities

Classification trees are a popular statistical tool with multiple applications. Recent advancements of traditional classification trees, such as the approach of classification trees based on imprecise probabilities by Abellán and Moral (2005), effectively address their tendency to overfitting. However, another flaw inherent in traditional classification trees is not eliminated by the imprecise probability approach: Due to a systematic finite sample-bias in the estimator of the entropy criterion employed in variable selection, categorical predictor variables with low information content are preferred if they have a high number of categories. Mechanisms involved in variable selection in classification trees based on imprecise probabilities are outlined theoretically as well as by means of simulation studies. Corrected estimators are proposed, which prove to be capable of reducing estimation bias as a source of variable selection bias.