The Neglected Error: False Negatives and the Case for Validating Eliminations

TL;DR

This paper highlights the overlooked risk of false negatives in forensic firearm comparisons, emphasizing the need for validation and transparent error reporting of eliminations to improve scientific rigor and legal fairness.

Contribution

It advocates for empirical validation of eliminations, including false negative rates, and proposes policy reforms to enhance forensic reliability and transparency.

Findings

Eliminations can function as de facto identifications in closed pools.

Most validity studies report only false positive rates, neglecting false negatives.

Policy recommendations include balanced error reporting and validation of intuitive judgments.

Abstract

This article examines the overlooked risk of false negative errors arising from eliminations in forensic firearm comparisons. While recent reforms in forensic science have focused on reducing false positives, eliminations--often based on class characteristics or intuitive judgments--receive little empirical scrutiny despite their potential to exclude true sources. In cases involving a closed pool of suspects, eliminations can function as de facto identifications, introducing serious risk of error. A review of existing validity studies reveals that many report only false positive rates, failing to provide a complete assessment of method accuracy. This asymmetry is reinforced by professional guidelines, such as those from AFTE, and echoed in major government reports, including those from NAS and PCAST. The article argues that eliminations, like identifications, must be validated through rigorous testing and reported with transparent error rates. It further cautions against the use of "common sense" eliminations in the absence of empirical support and highlights the dangers of contextual bias when examiners are aware of investigative constraints. Five policy recommendations are proposed to improve the scientific treatment and legal interpretation of eliminations, including balanced reporting of false positive and false negative rates, validation of intuitive judgments, and clear warnings against using eliminations to infer guilt in closed-pool scenarios. Without reform, eliminations will continue to escape scrutiny, perpetuating unmeasured error and undermining the integrity of forensic conclusions.