This study measured examiner (not laboratory) error rates for false identifications and false eliminations when comparing one unknown cartridge case to a collection of three known cartridge cases.
The study found that the rate of false negatives (incorrect decision of no match) was quite low (0.367 percent), with the error distributed across examiners of various backgrounds (State, Federal, local, private, etc.). The overall rate for false positives (incorrect match decisions) was significantly higher (1.01 percent); however most of these errors were reported by a small number of examiners. The overall rate is best interpreted as an average of widely varying individual rates. The participating examiners were provided with known positive and known negatives from independent groups of samples, providing independent measurements of a false positive rate and independent measurements of a false negative rate. This allowed the study to measure both rates and uncertainties in those rates. Responses were received from 218 participating examiners. The volunteer active examiners were members of the Association of Firearm and Toolmark Examiners or were working in laboratories that participate in the Association. 3 tables, 7 references, and appended details and samples of study materials