Research Article Volume 3 Issue 5 March 2017 DOI: 10.19080/JFSCI.2017.03.555601 J Forensic Sci & Criminal Inves Copyright © All rights are reserved by Michelle Cowley ‘The Innocent v The Fickle Few’: How Jurors Understand Random-Match-Probabilities and Judges’ Directions when Reasoning about DNA and Refuting Evidence *Michelle Cowley Royal Statistical Society, England Submission: March 12, 2017; Published: March 31, 2017 *Corresponding author: Michelle Cowley, Royal Statistical Society, Royal Statistical Society Fellow, Errol St., London, EC1Y 8LX, England, Tel: ; Email: J Forensic Sci & Criminal Inves 3(5): JFSCI.MS.ID.555601 (2017) 001 Introduction The power of DNA evidence in convicting the guilty and exonerating the innocent is well established [4,5]. The probative value of DNA evidence has been held up as a most valuable ‘Sword and Shield’ of criminal justice, and is now on a par with fingerprint evidence in identifying or eliminating suspects in a criminal trial [6]. DNA evidence is largely considered one of the greatest advances in the search for truth since the cross- examination [1], yet its presentation as a random-match- probability makes it one of the most complex sorts of evidence for people to assign appropriate probative value to [3,7]. Thus, if DNA matches are not 100% conclusive [8], and legal practitioners question whether everyday reasoners, such as jurors, can think about DNA evidence in terms of a random-match-probability in a way that is consonant with the statistical reasoning essential for reasoning accurately about probabilistic information [9], then we must find out more about what factors affect rational juror reasoning about DNA evidence. Consider what happened in the media following the now well-known disappearance case of Madeleine McCann [10], the child who went missing from a holiday apartment in Portugal in 2007 1 . Although what happened has never been definitively discovered, the media speculation focusing on the case in those early days and weeks of the investigation took a turn for the worst by theorizing that the child’s parents killed her rather than more explicitly theorizing about the possibility of child abduction. Due to disproportionate focus on Madeleine’s DNA evidence found in the apartment Abstract DNA evidence is one of the most significant modern advances in the search for truth since the cross examination, but its format as a random-match-probability makes it difficult for people to assign an appropriate probative value [1]. While Frequentist theories propose that the presentation of the match as a frequency rather than a probability facilitates more accurate assessment [2], Exemplar-Cueing Theory predicts that the subjective weight assigned may be affected by the frequency or probability format, and how easily examples of the event, i.e., ‘exemplars’, are generated from linguistic cues that frame the match in light of further evidence [3]. This paper presents two juror research studies to examine the difficulties that jurors have in assigning appropriate probative value to DNA evidence when contradictory evidence is presented. Study 1 showed that refuting evidence significantly reduced guilt judgments when exemplars were linguistically cued, even when the probability match and the refuting evidence had the same objective probative value. Moreover, qualitative reason for judgment responses revealed that interpreting refuting evidence was found to be complex and not necessarily reductive; refutation was found indicative of innocence or guilt depending on whether exemplars have been cued or not. Study 2 showed that the introduction of judges’ directions to linguistically cue exemplars, did not increase the impact of refuting evidence beyond its objective probative value, but less guilty verdicts were returned when jurors were instructed to consider all possible explanations of the evidence. The results are discussed in light of contradictory frequentist and exemplar-cueing theoretical positions, and their real-world consequences. Keywords: DNA Evidence; Random-Match-Probability; Juror Decision-Making; Exemplar-Cueing Theory; Frequentist Theories; Reasoning and Rationality