Validity and reliability of forensic firearm examiners

Area of Science:

• Forensic Science
• Firearms Examination
• Ballistics

Background:

• Forensic firearm examiners assess cartridge cases to determine if they originated from the same firearm.
• The validity and reliability of these expert judgments are crucial for the justice system.
• Comparison with automated methods is essential for evaluating and improving forensic analysis.

Purpose of the Study:

• To evaluate the validity and reliability of forensic firearm examiners' judgments on cartridge case origins.
• To compare the performance of human examiners with a computer-based method.
• To assess the calibration of examiners' expressed degrees of evidential support.

Main Methods:

• Analysis of striation patterns on firing pin aperture shear marks from 400 test shots from 200 Glock pistols.
• Comparison of these features using a computer-based method.
• Seventy-seven firearm examiners judged 60,000 comparisons, indicating source (same/different) and evidential support.

Main Results:

• Firearm examiners exhibited high true positive (sensitivity) and true negative (specificity) rates.
• Examiners were more accurate in identifying different-source comparisons than same-source comparisons.
• Examiners' reported degrees of evidential support were not well-calibrated, indicating overconfidence.

Conclusions:

• While examiners are generally proficient, their overconfidence necessitates improved calibration of evidential strength judgments.
• Performance feedback and potentially combining human and computer-based methods could enhance overall validity.
• The study highlights areas for improvement in training and methodology for forensic firearm examination.