RR: The Validity of Cartridge Case Comparison Conclusions Under Field-Based Conditions

Iowa State University, Ames IA

Investigators

Abstract

The National Research Council in 2009 called for scientists to quantify the validity of forensic techniques under realistic, field-based conditions. This call was prompted because it is increasingly apparent there are potential gaps in knowledge about the validity of a broad range of forensic techniques. Yet, the results of forensic science are often viewed as objective, and as such they are accepted and used by law enforcement and courts, and beyond. This project will investigate and quantify the validity of fired gun cartridge case comparison, a commonly used forensic technique. Because this technique relies on visual inspection of fired cartridge cases, it is a subjective process that is susceptible to human judgment error. However, even though this technique is subjective, it can still be a valid technique if the rate of human judgment error is low under a variety of field-based conditions. Because all forensic conclusions involve some degree of uncertainty, this research can advance understanding about the validity of forensic science. The project will use a controlled experiment under field-based conditions to address whether conventional peer-review procedures effectively discover forensic errors before they are communicated to law enforcement and the courts, and whether the rate at which forensic errors occur varies based on the quality of toolmarks produced by different firearm brands. The project is grounded in psychological theory related to decision-making and cognitive processing, and it accords with calls for rigorous scientific tests to evaluate the validity of forensic techniques. The research brings scientific methods (including experimental manipulations) to the study of the validity of cartridge case comparisons, including the robustness (in the context of conventional peer-review procedures) and reliability (across different field-based conditions) of this technique. This research has the potential to transform forensic science practices by emphasizing the importance of communicating the degree of uncertainty that characterizes forensic conclusions, while identifying potential threats to conventional peer-review procedures. This project is jointly supported by National Science Foundation and the National Institute of Justice.