Juror comprehension of DNA evidence: the effect of timing and judicial instruction on coherence-shifts

Abstract

This project aims to investigate whether an attempt to mitigate bias perceptions of DNA evidence by manipulating the timing of the forensic evidence and judicial instruction will be effective. Mock-jurors have demonstrated that they often do not attribute appropriate strength to forensic evidence during a trial. It is known that jurors reason by creating a story (Pennington & Hastie, 1986; 1992; 1993), however, little is known about the inferential process by which jurors actually integrate the competing and contradictory pieces of evidence. Coherence-shifts have been referred to under many different names, including; inference to the best explanation, pre-decisional information distortion and related concepts such as the assimilation hypothesis and explanatory coherence which also fit within a paradigm of this study’s interest. These models indicate (herein after referred to as ‘coherence-shifts’), that early during the decision making process, a preferred decision emerges. The individual pieces of evidence in support of this preferred decision thereafter are attributed more weight, causing a 'coherence-shift.' This has the potential implication that the prosecution have an inherent advantage over the defence in presenting their evidence first. Although this is an institutional process which cannot be changed and is needed (the prosecution need to establish their case first), it may be the case that even within the prosecution case presenting DNA evidence early contributes to the distortion and inappropriate evaluation of that evidence. Judicial instructions have been studied with mixed results. Typically, the judicial instructions are given later in the trial, despite studies showing that they are ineffective, with some studies finding that judicial instructions given at the end of the trial have no effect at all (Dartnall & Goodman-Delahunty, 2006). However, this may be due to a lack of engagement or ability to apply the instruction to the decision process on behalf of the mock-jurors. Kassin & Wrightsman (1979) found judicial instruction given at the beginning of the trial to be more effective, resulting in fewer guilty verdicts. However, there is a gap in the literature on examining instruction around fallacious reasoning around DNA evidence. This research aims to contribute to the knowledge on juror comprehension of forensic evidence by filling a gap in the literature on timing of forensic evidence. It aims to assess if a judicial instruction given early in the trial can aid jurors to better evaluate DNA evidence. This could justify more research on a connectionist model of inferential reasoning, if results indicate that presenting the same forensic evidence at different time points impacts on decisions