Determining the Number of Test Fires Needed to Represent the Variability Present Within a Firearm
Date of Graduation
Eberly College of Arts and Sciences
Forensic and Investigative Science
Many studies have been performed in recent years in the field of firearm examination with the goal of providing an objective method for comparisons of fired cartridge cases. To date there has been no research to support the number of test fires needed to represent the variability present within a firearm. When a suspect firearm is submitted to a firearm examiner, test fires are performed to collect fired cartridge cases for comparison purposes. Typically, two to four test fires are performed for every firearm. The recovered cartridge cases are compared to each other to determine which characteristics from the firearm are reproducing, and then compared to any cartridge cases collected at a crime scene. The aim of this research was to determine the number of test fires firearm examiners should perform when a suspect firearm is submitted to the lab to balance cartridge case acquisition time with performance accuracy. Each firearm in the IBIS database at West Virginia University is represented by 100 fired cartridge case entries. This translates to about 5,000 breech face and firing pin match scores. Random samples of scores were taken separately from the breech face match score and firing pin match score lists. This subset was compared to the total match distribution of the firearm using a hybrid equivalence test to determine if the subset of similarity scores were statistically equivalent to the larger distribution of scores. The hybrid equivalence method was composed of three tests: the Kolmogorov-Smirnov two-sample test, the Mann-Whitney equivalence test, and the Fligner-Killeen test. A combination of the results of each test was utilized to determine equivalence or non-equivalence between the sampled and match distributions.;For the sampled distribution to remain above 80% equivalent to the match distribution, a minimum of 15 cartridge cases should be used to model the match distribution. Thirty cartridge cases is a conservative estimate, being that it is enough to be 100% equivalent to the actual firearm match distribution of 100 fired cartridge cases.
Law, Eric, "Determining the Number of Test Fires Needed to Represent the Variability Present Within a Firearm" (2016). Graduate Theses, Dissertations, and Problem Reports. 6043.