Contrastive dissimilarity: optimizing performance on imbalanced and limited data sets

A primary challenge in pattern recognition is imbalanced datasets, resulting in skewed and biased predictions. This problem is exacerbated by limited data availability, increasing the reliance on expensive expert data labeling. The study introduces a novel method called contrastive dissimilarity, which combines dissimilarity-based representation with contrastive learning to improve classification performance in imbalance and data scarcity scenarios. Based on pairwise sample differences, dissimilarity representation excels in situations with numerous overlapping classes and limited samples per class. Unlike traditional methods that use fixed distance functions like Euclidean or cosine, our proposal employs metric learning with contrastive loss to estimate a custom dissimilarity function. We conducted extensive evaluations in 13 databases across multiple training–test splits. The results showed that this approach outperforms traditional models like SVM, random forest, and Naive Bayes, particularly in settings with limited training data.