Multi-Class Learning by Smoothed Boosting

AdaBoost.OC has been shown to be an effective method in boosting “weak” binary classifiers for multi-class learning. It employs the Error-Correcting Output Code (ECOC) method to convert a multi-class learning problem into a set of binary classification problems, and applies the AdaBoost algorithm to solve them efficiently. One of the main drawbacks with the AdaBoost.OC algorithm is that it is sensitive to the noisy examples and tends to overfit training examples when they are noisy. In this paper, we propose a new boosting algorithm, named “MSmoothBoost”, which introduces a smoothing mechanism into the boosting procedure to explicitly address the overfitting problem with AdaBoost.OC. We proved the bounds for both the empirical training error and the marginal training error of the proposed boosting algorithm. Empirical studies with seven UCI datasets and one real-world application have indicated that the proposed boosting algorithm is more robust and effective than the AdaBoost.OC algorithm for multi-class learning.