The effect of timing of DNA and judicial instruction on coherence-shifts during mock-juror evaluation of DNA evidence

Abstract

The integrity of a trial rests on the jury’s ability to objectively and accurately evaluate the facts, yet a large body of research indicates jurors do not reason objectively. The Story Model (Pennington & Hastie, 1988) Explanatory Coherence (Thaggard, 1989) and Coherence-Based Reasoning (Simon, 2004) were used as the theoretical basis for the current study. Using a 2*2*2 experimental design 257 participants, acting as mock-jurors read a criminal trial transcript and rated the evidence twice. Here we show that DNA presented early by the prosecution is associated with greater coherence-shifting. A recency effect was found for initial ratings of DNA evidence. This supports the literature that jurors do not reason objectively; however, the two cognitive effects appear to work in opposite directions, resulting in homogenous ratings of that same evidence by deliberation. DNA timing did not impact confidence ratings. Further, DNA did not inflate subsequent evidence, failing to replicate the recent assimilation hypothesis (Rassin, 2017). Pre-trial instruction was associated with better understanding of DNA evidence and lower ratings of prosecution DNA. Inconsistencies in findings indicate that the cognitie processes may be different for the prosecution and the defence. Limitations, including a lack of power, and implications the theoretical frameworks and the legal system are discussed. Keywords: coherence-shift; DNA evidence; juror reasoning; judicial instruction