MDAS: A Diagnostic Approach to Assess the Quality of Data Splitting in Machine Learning

Abstract

In the field of machine learning, model performance is usually assessed by randomly splitting data into training and test sets. Different random splits, however, can yield markedly different performance estimates, so a genuinely good model may be discarded or a poor one selected purely due to an unlucky partition. This motivates a principled way to diagnose the quality of a given data split. We propose a diagnostic framework based on a new discrepancy measure, the Mahalanobis Distribution Alignment Score (MDAS). MDAS is a symmetric dissimilarity measure between two multivariate samples, rather than a strict metric. MDAS captures both mean and covariance differences and is affine invariant. Building on this, we construct a Monte Carlo test that evaluates whether an observed split is statistically compatible with typical random splits, yielding an interpretable p-value for split quality. Using several real data sets, we study the relationship between MDAS and model robustness, including its association with the normalized Akaike information criterion. Finally, we apply MDAS to compare existing state-of-the-art deterministic data-splitting strategies with standard random splitting. The experimental results show that MDAS provides a simple, model-agnostic tool for auditing data splits and improving the reliability of empirical model evaluation.