Towards a Theoretical Framework for Ensemble Classification

Ensemble learning schemes such as AdaBoost and Bagging enhance the performance of a single classifier by combining predictions from multiple classifiers of the same type. The predictions from an ensemble of diverse classifiers can be combined in related ways, e.g. by voting or simply by selecting the best classifier via cross-validation a technique widely used in machine learning. However, since no ensemble scheme is always the best choice, a deeper insight into the structure of meaningful approaches to combine predictions is needed to achieve further progress. In this paper we offer an operational reformulation of common ensemble learning schemes Voting, Selection by Crossvalidation (X-Val), Grading and Bagging as a Stacking scheme with appropriate parameter settings. Thus, from a theoretical point of view all these schemes can be reduced to Stacking with an appropriate combination method. This result is an important step towards a general theoretical framework for the field of ensemble learning.