Ordinal Forests


The ordinal forest method is a random forest–based prediction method for ordinal response variables. Ordinal forests allow prediction using both low-dimensional and high-dimensional covariate data and can additionally be used to rank covariates with respect to their importance for prediction. An extensive comparison study reveals that ordinal forests tend to outperform competitors in terms of prediction performance. Moreover, it is seen that the covariate importance measure currently used by ordinal forest discriminates influential covariates from noise covariates at least similarly well as the measures used by competitors. Several further important properties of the ordinal forest algorithm are studied in additional investigations. The rationale underlying ordinal forests of using optimized score values in place of the class values of the ordinal response variable is in principle applicable to any regression method beyond random forests for continuous outcome that is considered in the ordinal forest method.

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The author thanks Giuseppe Casalicchio for proofreading and comments and Jenny Lee for language corrections. This work was supported by the German Science Foundation (DFG-Einzelförderung BO3139/6-1 to Anne-Laure Boulesteix).

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Correspondence to Roman Hornung.

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Hornung, R. Ordinal Forests. J Classif 37, 4–17 (2020). https://doi.org/10.1007/s00357-018-9302-x

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  • Prediction
  • Ordinal response variable
  • Covariate importance ranking
  • Random forest