Active Learning for Stacking and AdaBoost-Related Models

Ensemble learning (EL) has become an essential technique in machine learning that can significantly enhance the predictive performance of basic models, but it also comes with an increased cost of computation. The primary goal of the proposed approach is to present a general integrative framework that allows for applying active learning (AL) which makes use of only limited budget by selecting optimal instances to achieve comparable predictive performance within the context of ensemble learning. The proposed framework is based on two distinct approaches: (i) AL is implemented following a full scale EL, which we call the ensemble learning on top of active learning (ELTAL), and (ii) apply the AL while using the EL, which we call the active learning during ensemble learning (ALDEL). Various algorithms for ELTAL and ALDEL are presented using Stacking and Boosting with various algorithm-specific query strategies. The proposed active learning algorithms are numerically illustrated with the Support Vector Machine (SVM) model using simulated data and two real-world applications, evaluating their accuracy when only a small number instances are selected as compared to using full data. Our findings demonstrate that: (i) the accuracy of a boosting or stacking model, using the same uncertainty sampling, is higher than that of the SVM model, highlighting the strength of EL; (ii) AL can enable the stacking model to achieve comparable accuracy to the SVM model using the full dataset, with only a small fraction of carefully selected instances, illustrating the strength of active learning.