The Persuasive Powers of DNA: An Experimental Study in Perceptions of Expert Evidence

Abstract

This article presents the results of an experimental study where mock-jurors were tasked with interpreting the presentation of DNA evidence. The 200 university student participants were exposed to one of five murder scenarios where the information about the DNA evidence was manipulated. The results showed that participants were more likely to convict when the DNA match statistic was presented as a probability (0.1%) and focused on the defendant, less likely to convict when it was presented as a frequency (1 in 1,000) and focused on a broader reference group, and even less likely in the control scenario with no DNA evidence. The forensic knowledge of participants was also explored, and more than three-quarters demonstrated reasonable understanding of the individuating capacity of DNA evidence. Participants recognized that while DNA has the capacity to determine guilt, it is insufficient on its own to convict or acquit. The implications for the presentation of expert testimony and judicial instruction are canvassed, and the broader ramifications for the education of jurors and legal personnel are discussed.