Journal
CHEMOMETRICS AND INTELLIGENT LABORATORY SYSTEMS
Volume 217, Issue -, Pages -Publisher
ELSEVIER
DOI: 10.1016/j.chemolab.2021.104399
Keywords
Likelihood ratio; Forensic glass comparison; LA-ICP-MS; Variational autoencoder; Warped Gaussian mixture; Heavy-tailed
Categories
Funding
- Spanish Ministerio de Educacion, Cultura y Deporte
- National Institute of Justice, Office of Justice Programs, U.S. Department of Justice to Florida International University [2018-DU-BX-0194]
- Spanish Ministerio de Educacion, Cultura y Deporte [RTI2018-098091-B-I00]
- FPI-UPV [825111]
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The calibration of likelihood ratios generated using previous models is crucial for realistic reporting of glass evidence comparisons. Our proposed models, which incorporate heavy-tailed within-source variability and probabilistic machine learning algorithms for between-source variability, outperform previous LR models and show superior performance in calibration and robustness.
The computation of likelihood ratios (LR) to measure the weight of forensic glass evidence with LA-ICP-MS data directly in the feature space without computing any kind of score as an intermediate step is a complex problem. A probabilistic two-level modeling of the within-source and between-source variability of the glass samples is needed in order to compare the elemental profiles measured from glass recovered from a suspect or a crime scene and compared to glass samples of a known source of origin. Calibration of the likelihood ratios generated using previously reported models is essential to the realistic reporting of the value of the glass evidence comparisons. We propose models that outperform previously proposed feature-based LR models, in particular by improving the calibration of the computed LRs. We assume that the within-source variability is heavy-tailed, in order to incorporate uncertainty when the available data is scarce, as it typically happens in forensic glass comparison. Moreover, we address the complexity of the between-source variability by the use of probabilistic machine learning algorithms, namely a variational autoencoder and a warped Gaussian mixture. Our results show that the overall performance of the likelihood ratios generated by our model is superior to classical approaches, and that this improvement is due to a dramatic improvement in the calibration despite some loss in discriminating power. Moreover, the robustness of the calibration of our proposal is remarkable.
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