Skip to content

Treatment of inconclusives in the AFTE range of conclusions

Journal: Law, Probability and Risk
Published: 2021
Primary Author: Heike Hofmann
Secondary Authors: Susan Vanderplas, Alicia Carriquiry
Research Area: Firearms and Toolmarks

In the past decade, and in response to the recommendations set forth by the National Research Council Committee on Identifying the Needs of the Forensic Sciences Community (2009), scientists have conducted several black-box studies that attempt to estimate the error rates of firearm examiners. Most of these studies have resulted in vanishingly small error rates, and at least one of them (D. P. Baldwin, S. J. Bajic, M. Morris, and D. Zamzow. A Study of False-Positive and False-Negative Error Rates in Cartridge Case Comparisons. Technical report, Ames Lab IA, Performing, Fort Belvoir, VA, April 2014.) was cited by the President’s Council of Advisors in Science and Technology (PCAST) during the Obama administration, as an example of a well-designed experiment. What has received little attention, however, is the actual calculation of error rates and in particular, the effect of inconclusive findings on those error estimates. The treatment of inconclusives in the assessment of errors has far-reaching implications in the legal system. Here, we revisit several black-box studies in the area of firearms examination, investigating their treatment of inconclusive results. It is clear that there are stark differences in the rate of inconclusive results in regions with different norms for training and reporting conclusions. More surprisingly, the rate of inconclusive decisions for materials from different sources is notably higher than the rate of inconclusive decisions for same-source materials in some regions. To mitigate the effects of this difference we propose a unifying approach to the calculation of error rates that is directly applicable in forensic laboratories and in legal settings.

Related Resources

Exploration of Subclass Characteristics Manufacturing

Exploration of Subclass Characteristics Manufacturing

A webinar presented during the Forensic Technology Center of Excellence (FTCoE0 Firearm and Toolmark webinar series on the progress of our CSAFE project. This study assesses the production of subclass…
Surveying Practicing Firearm Examiners

Surveying Practicing Firearm Examiners

A sample (n = 79) of practicing firearm and toolmark examiners was queried about casework as well as their views about the potential role that statistics might play in future…
Blind testing in firearms: Preliminary results from a blind quality control program

Blind testing in firearms: Preliminary results from a blind quality control program

Open proficiency tests meet accreditation requirements and measure examiner competence but may not represent actual casework. In December 2015, the Houston Forensic Science Center began a blind quality control program…
Ruger LCP Study: a two-pronged approach

Ruger LCP Study: a two-pronged approach

This study started as an attempt to take a closer look at the rifling observed in the 380 Auto Ruger LCP pistol