From Classical Machine Learning to Tabular Foundation Models: An Empirical Investigation of Robustness and Scalability Under Class Imbalance in Emergency and Critical Care

Millions of patients pass through emergency departments and intensive care units each year, where clinicians must make high-stakes decisions under time pressure and uncertainty. Machine learning could support these decisions by predicting deterioration, guiding triage, and identifying rare but serious outcomes. Yet clinical tabular data are often highly imbalanced, biasing models toward majority classes. Building methods that are robust to imbalance and efficient enough for deployment remains a practical challenge.We investigated seven model families on imbalanced tabular data from MIMIC-IV-ED and eICU: Decision Tree, Random Forest, XGBoost, TabNet, TabResNet, TabICL, and TabPFN v2.6. TabResNet was designed as a lightweight alternative to TabNet. Models were evaluated using weighted F1-score, robustness to increasing imbalance, and computational scalability across seven prediction tasks.Performance varied by dataset. On MIMIC-IV-ED, TabPFN v2.6 and TabICL achieved the strongest average weighted F1 ranks, with XGBoost and TabResNet remaining competitive. On eICU, XGBoost performed best overall, followed by other tree-based methods, while foundation models ranked in the middle. TabNet showed the steepest performance decline as imbalance increased and the highest computational cost. TabResNet consistently outperformed TabNet, but did not surpass the best ensemble models. Classical and tree-based methods scaled most favourably with dataset size, while foundation models achieved low per-task cost through their inference-based paradigm.No single model family dominated across both datasets and tasks. However, tabular foundation models showed promise by combining competitive performance at low computational cost. If this efficiency generalizes to broader clinical settings, it could help lower the barrier to adaptive decision support in resource-constrained environments.