Beyond predictive accuracy: Statistical validation of feature importance in biomedical machine learning

In medical machine learning (ML), a fundamental methodological distinction exists between optimizing model performance for predictive tasks and pursuing causal inference for mechanistic interpretation. Achieving high predictive accuracy does not necessarily imply that a model can uncover the true physiological mechanisms underlying the data. This letter addresses a critical interpretational challenge in medical machine learning, building upon Yuyang Yan et al.'s valuable work on exacerbation classification in asthma and COPD. While their multi-feature fusion model, particularly comprising models such as K-Nearest Neighbors (KNN), Support Vector Machines (SVM), Random Forest (RF), and Bidirectional Long Short-Term Memory (BiLSTM) demonstrates high predictive accuracy for respiratory exacerbations, we highlight that such performance alone does not guarantee reliable insights into feature importance. Complex tree-based models like RF, when interpreted via methods like SHapley Additive exPlanations (SHAP), can exhibit inherent biases, overemphasizing features used in early splits and reflecting what is important for their specific prediction rather than the true underlying physiological drivers. Validating feature importance remains challenging without ground truth, as different models often yield varying rankings. We argue that solely relying on model-dependent interpretations risks misrepresenting the actual mechanisms of complex medical phenomena. Therefore, we advocate for a robust analytical strategy that transcends mere predictive metrics. This involves a synergistic approach combining the predictive power of ML with impartial, complementary statistical methodologies-such as non-parametric correlation and mutual information-to ensure genuinely trustworthy scientific insights into the true drivers of respiratory exacerbations.