DNA Evidence: The Layperson’s Application

• In Event: The Impact of the Type and Strength of Evidence on Sentencing Decisions

Abstract

DNA evidence is being used more frequently, to the point now it can be the main or sometimes the only real circumstantial evidence admitted at trial. The Australian High Court recently rejected the appeal in Aytugrul and held it was acceptable to express the DNA results as either a frequency ratio or as an exclusion percentage. This research sought to explore whether the way the results were presented could affect the verdict in a criminal case. Using online survey data collected from the general public who were eligible for jury duty in Australia (n = 258), participants completed two vignettes. The two different forensic results were manipulated in a 2x2 between group designs, with participants being randomly assigned to conditions. Results showed the way evidence was presented was sometimes statistically significant, and when not, the relationship was going in the predicted direction. Specifically when evidence was presented as an exclusion percentage, participants were sometimes more likely to convict then when presented with frequency ratio evidence. Further, the perceived trustworthiness of evidence was a predictor of verdict. This research is important as the consequences of misleading evidence can have serious consequences for the victim, the accused and the criminal justice system.

Author

• Jessica Ritchie, Griffith University