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Adversarial Forensic Science Experts: An Empirical Study of Jury Deliberation

Abstract Surprisingly little is known about ways that juries resolve differences of opinion between competing scientific forensic experts. Concerns have been raised that juries defer unduly to scientific experts and are susceptible to the ‘white coat effect’. The study reported in this article examined jury decision-making in the context of a live, simulated homicide trial that incorporated traditional legal procedural safeguards against jury error: cross-examination, the use of rebuttal expert witnesses, judicial directions and group deliberation. Following the presentation of opposing expert opinions on analyses of trace evidence, 12 juries deliberated to a verdict. Deliberation transcripts were systematically analysed to discern prominent topics discussed in the jury room. Using a text-mining method, shifts in deliberation focus were explored in response to two interventions: (a) a judicial caution about the non-binding nature of expert illustrative visual aids; and (b) uneven versus evenly balanced rebuttal expert evidence. Results indicated that juries were not deferential to the experts, but did not ignore them either. They found the experts' sophisticated interactive visual aids useful, but appropriately discerned that the scientific evidence did not resolve the issues before them. No evidence emerged for ‘the white coat effect’. Excerpts from deliberations substantiated the quantitative outcomes.