Evaluation methods for ordinal classification

Abstract

Ordinal classification is a form of multi-class classification where there is an inherent ordering between the classes, but not a meaningful numeric difference between them. Little attention has been paid as to how to evaluate these problems, with many authors simply reporting accuracy, which does not account for the severity of the error. Several evaluation metrics are compared across a dataset for a problem of classifying user reviews, where the data is highly skewed towards the highest values. Mean squared error is found to be the best metric when we prefer more (smaller) errors overall to reduce the number of large errors, while mean absolute error is also a good metric if we instead prefer fewer errors overall with more tolerance for large errors. © 2009 Springer Berlin Heidelberg.