Relative discrimination criterion – A novel feature ranking method for text data

High dimensionality of text data hinders the performance of classifiers making it necessary to apply feature selection for dimensionality reduction. Most of the feature ranking metrics for text classification are based on document frequencies (df) of a term in positive and negative classes. Considering only document frequencies to rank features favors terms frequently occurring in larger classes in unbalanced datasets. In this paper we introduce a new feature ranking metric termed as relative discrimination criterion (RDC), which takes document frequencies for each term count of a term into account while estimating the usefulness of a term. The performance of RDC is compared with four well known feature ranking metrics, information gain (IG), CHI squared (CHI), odds ratio (OR) and distinguishing feature selector (DFS) using support vector machines (SVM) and multinomial naive Bayes (MNB) classifiers on four benchmark datasets, namely Reuters, 20 Newsgroups and two subsets of Ohsumed dataset. Our results based on macro and micro F1 measures show that the performance of RDC is superior than the other four metrics in 65% of our experimental trials. Also, RDC attains highest macro and micro F1 values in 69% of the cases.