Strength of Firearms Comparisons
Author Information
Author(s): Aggadi Nada, Zeller Kimberley, Busey Tom
Primary Institution: Department of Psychological and Brain Sciences, Indiana University‐Bloomington
Hypothesis
Can error rate studies provide a quantitative measure of the strength of evidence in firearms comparisons?
Conclusion
The study found that current verbal scales used by forensic examiners overstate the strength of evidence in firearms comparisons.
Supporting Evidence
- Likelihood ratios can be as low as less than 10, indicating weak evidence.
- The current verbal conclusion scale may imply a strength of evidence of 10,000 or greater.
- Examiners' interpretations of evidence strength can vary significantly.
Takeaway
This study shows that the way forensic experts say whether a bullet matches a gun can be misleading, and suggests using numbers instead to show how strong the evidence really is.
Methodology
The study reanalyzed data from error rate studies using an ordered probit model to calculate likelihood ratios for firearms evidence.
Potential Biases
Examiners may overstate evidence strength due to personal biases or misinterpretation of verbal scales.
Limitations
The study relies on existing data from error rate studies, which may not fully represent all forensic contexts.
Participant Demographics
173 forensic examiners participated in the study.
Digital Object Identifier (DOI)
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