Empirical Evaluation of Semi-Supervised Naive Bayes for Active Learning
Date and time: 11th October 13:00-14:00
Location: Queens 1.03
Title: Empirical Evaluation of Semi-Supervised Naive Bayes for Active Learning
Speaker: Awat Saeed
Institution: School of Computing Sciences, UEA
Organiser: Dr. Michal Mackiewicz
Active learning aims to minimise the amount of labelled data required by using the model to direct labelling of the most informative unlabelled examples to give the greatest improvement in the subsequence generation of model, but the key difficulty with active learning is that the initial model often gives a poor direction for labelling the unlabelled data in the early stages. However, using both labelled and unlabelled data with semi-supervised learning might result in a better initial model. In this talk, we describe an empirical evaluation of semi-supervised and active learning individually, and in combination for the naive Bayes classifier. For this purpose, a suite of benchmark datasets are used and the learning curves for experiments to compare the performance of each approach are presented. First, we show that the semi-supervised naive Bayes does not improve the performance of the naive Bayes classifier. Subsequently, a down-weighting technique is used to control the influence of the unlabelled data, but again this does not improve performance. In the next experiment, a novel algorithm is proposed by using a sigmoid transformation to recalibrate the overly confident prediction of the naive Bayes classifier. This algorithm does not significantly improve on the naive Bayes classifier, but at least does improve the semi-supervised naive Bayes classifier somewhat. In the final experiment we investigate the effectiveness of the combination of active and semi-supervised learning and empirically illustrate when the combination does work, and when does not.