Evaluation of distance-based approaches for forensic comparison: Application to hand odor evidence
This addresses the challenge of evaluating high-dimensional evidence like hand odor profiles for forensic practitioners, though it is incremental as it compares existing method types on a new application.
The paper tackled the problem of distinguishing same-source vs. different-source hypotheses in forensic science using distance-based approaches, finding that indirect methods (e.g., logistic regression) significantly outperformed direct methods in sensitivity, specificity, and robustness on hand odor evidence, with empirical results from 534 subjects and 1690 odor traces.
The issue of distinguishing between the same-source and different-source hypotheses based on various types of traces is a generic problem in forensic science. This problem is often tackled with Bayesian approaches, which are able to provide a likelihood ratio that quantifies the relative strengths of evidence supporting each of the two competing hypotheses. Here, we focus on distance-based approaches, whose robustness and specifically whose capacity to deal with high-dimensional evidence are very different, and need to be evaluated and optimized. A unified framework for direct methods based on estimating the likelihoods of the distance between traces under each of the two competing hypotheses, and indirect methods using logistic regression to discriminate between same-source and different-source distance distributions, is presented. Whilst direct methods are more flexible, indirect methods are more robust and quite natural in machine learning. Moreover, indirect methods also enable the use of a vectorial distance, thus preventing the severe information loss suffered by scalar distance approaches.Direct and indirect methods are compared in terms of sensitivity, specificity and robustness, with and without dimensionality reduction, with and without feature selection, on the example of hand odor profiles, a novel and challenging type of evidence in the field of forensics. Empirical evaluations on a large panel of 534 subjects and their 1690 odor traces show the significant superiority of the indirect methods, especially without dimensionality reduction, be it with or without feature selection.