Ordinal Decision Trees are a machine learning approach specifically designed to handle ordinal classification tasks, where the labels exhibit a natural order. Unlike nominal classification, which treats all classes as equally distinct, ordinal classification takes the ordinal relationship into account, producing more accurate and relevant results. This is particularly critical in applications where the magnitude of classification errors has implications. Despite their importance, ordinal classification problems are often tackled using nominal methods, leading to suboptimal solutions. This work conducts an experimental study of tree-based methodologies specifically designed to capture ordinal relationships. A comprehensive survey of ordinal splitting criteria is provided, standardizing the notations used in the literature for clarity. Three ordinal splitting criteria, Ordinal Gini (OGini), Weighted Information Gain (WIG), and Ranking Impurity (RI), are compared to the nominal counterparts of the first two (Gini and information gain), by incorporating them into a decision tree classifier. An extensive repository considering 45 publicly available OC datasets is presented, supporting the first experimental comparison of ordinal and nominal splitting criteria using well-known OC evaluation metrics. Statistical analysis of the results highlights OGini as the most effective ordinal splitting criterion to date.
Decision Trees
Ordinal Splitting Criteria
45 publicly available OC datasets
Ordinal Gini, Weighted Information Gain, Ranking Impurity
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Captures ordinal relationships, provides more accurate results
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Improved ordinal classification
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01/01/1970
01/01/1970
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