Improving the classification of extreme classes by means of loss regularisation and generalised beta distributions
This work addresses a specific challenge in ordinal classification for real-world applications where extreme class accuracy is critical, representing an incremental improvement over existing methods.
The paper tackles the problem of accurately classifying extreme classes in ordinal classification tasks by proposing a unimodal regularisation approach applicable to any loss function, which improves performance on the first and last classes while maintaining overall accuracy, as shown by superior average results on six datasets with a new metric and statistical analysis.
An ordinal classification problem is one in which the target variable takes values on an ordinal scale. Nowadays, there are many of these problems associated with real-world tasks where it is crucial to accurately classify the extreme classes of the ordinal structure. In this work, we propose a unimodal regularisation approach that can be applied to any loss function to improve the classification performance of the first and last classes while maintaining good performance for the remainder. The proposed methodology is tested on six datasets with different numbers of classes, and compared with other unimodal regularisation methods in the literature. In addition, performance in the extreme classes is compared using a new metric that takes into account their sensitivities. Experimental results and statistical analysis show that the proposed methodology obtains a superior average performance considering different metrics. The results for the proposed metric show that the generalised beta distribution generally improves classification performance in the extreme classes. At the same time, the other five nominal and ordinal metrics considered show that the overall performance is aligned with the performance of previous alternatives.