Artif Intell Rev (2008) 30:19–37 DOI 10.1007/s10462-009-9114-9 A review on the combination of binary classifiers in multiclass problems Ana Carolina Lorena · André C. P. L. F. de Carvalho · João M. P. Gama Published online: 13 August 2009 © Springer Science+Business Media B.V. 2009 Abstract Several real problems involve the classification of data into categories or classes. Given a data set containing data whose classes are known, Machine Learning algorithms can be employed for the induction of a classifier able to predict the class of new data from the same domain, performing the desired discrimination. Some learning techniques are orig- inally conceived for the solution of problems with only two classes, also named binary classification problems. However, many problems require the discrimination of examples into more than two categories or classes. This paper presents a survey on the main strategies for the generalization of binary classifiers to problems with more than two classes, known as multiclass classification problems. The focus is on strategies that decompose the original multiclass problem into multiple binary subtasks, whose outputs are combined to obtain the final prediction. Keywords Machine learning · Supervised learning · Multiclass classification A. C. Lorena (B ) Centro de Matemática, Computação e Cognição, Universidade Federal do ABC, Santo André, SP 09.210-170, Brazil e-mail: ana.lorena@ufabc.edu.br; aclorena@gmail.com A. C. P. L. F. de Carvalho Departamento de Ciências de Computação, Instituto de Ciências Matemáticas e de Computação, Universidade de São Paulo, Campus de São Carlos, Caixa Postal 668, São Carlos, SP 13560-970, Brazil e-mail: andre@icmc.usp.br J. M. P. Gama Laboratório de Inteligência Artificial e Ciência de Computadores, Universidade do Porto, 4150-190, Porto, Portugal e-mail: jgama@liacc.up.pt 123