Local Sparsity Control for Naïve Bayes with Extreme Misclassification Costs Aleksander Kolcz   View Paper (PDF)   Return to Research Session 4 [Cost Sensitive Learning] Abstract In applications of data mining characterized by highly skewed misclassification costs certain types of errors become virtually unacceptable. This limits the utility of a classifier to a range in which such constraints can be met. Naive Bayes, which has proven to be very useful in text mining applications due to high scalability, can be particularly affected. Although its 0/1 loss tends to be small, its misclassifications are often made with apparently high confidence. Aside from efforts to better calibrate Naive Bayes scores, it has been shown that its accuracy depends on document sparsity and feature selection can lead to marked improvement in classification performance. Traditionally, sparsity is controlled globally, and the result for any particular document may vary. In this work we examine the merits of local sparsity control for Naive Bayes in the context of highly asymmetric misclassification costs. In experiments with three benchmark document collections we demonstrate clear advantages of document-level feature selection. In the extreme cost setting, multinomial Naive Bayes with local sparsity control is able to outperform even some of the recently proposed effective improvements to the Naive Bayes classifier. There are also indications that local feature selection may be preferable in different cost settings. ©2006 Association for Computing Machinery