Feature-Based Likelihood Ratios for Forensic Science: Combining Neural Networks with Bayesian Probability Calculus
This study addresses the calibration challenges inherent in feature-based likelihood ratio (LR) models within forensic science, which frequently compromise the statistical interpretation of “similarity” and “typicality.” To overcome these limitations, this work proposes a bi-level model that integrates neural network gradient descent with Bayesian probability theory to generate well-calibrated, on-the-fly feature-based LRs. By restoring the LR as a comparative measure of similarity and typicality, the proposed framework achieves end-to-end calibration without requiring post-processing. Evaluated on glass fragment LA-ICP-MS data, the method yields a 4.5-fold improvement in the log-likelihood ratio cost (C_llr) over comparable systems, significantly outperforming existing feature-based LR approaches. These results establish an interpretable and highly reliable new paradigm for forensic evidence evaluation.