Evidentiary instructions improve mock juror assessment of feature-comparison evidence
| Published date | 01 July 2018 |
| DOI | 10.1177/1365712718783427 |
| Author | Eva Ribbers,Marika Linnéa Henneberg |
| Date | 01 July 2018 |
| Subject Matter | Articles |
Article
Evidentiary instructions
improve mock juror assessment
of feature-comparison evidence
Eva Ribbers
Department of Psychology, University of Portsmouth, Portsmouth, UK
Marika Linne
´a Henneberg
Institute of Criminal Justice Studies, University of Portsmouth, Portsmouth, UK
Abstract
Feature-comparison evidence has been introduced in court without sufficient scientific vali-
dation and has been at the heart of numerous miscarriages of justice. Juror assessment of such
evidence and the efficacy of evidentiary instructions were examined through a mock jury
experiment with case reports featuring either central or peripheral feature-comparison evi-
dence. In a case-control design (N ¼174), the test group was exposed to an evidentiary
instruction about the ear print evidence presented in the first case report (adapted from Rv
Dallagher [2002] EWCA Crim 1903) whereas the control group did not receive such an
instruction. The provision of this instruction resulted in a significant decrease in verdict
severity with a large effect size. For the second case report (based on RvGeorge (Barry) [2007]
EWCA Crim 2722), all subjects were asked to return verdicts based on circumstantial evi-
dence, gunpowder residue evidence and an evidentiary instruction about that gunpowder
residue evidence. Verdict severity increased significantly after the provision of gunpowder
residue evidence, followed by a subsequent reduction in verdict severity after the introduction
of an evidentiary instruction. Furthermore, there was a significant difference in verdict severity
between the test and control group, suggesting that the test group exhibited a scepticism effect
brought about by the initial evidentiary instruction about ear print evidence. This study
demonstrates that although mock jurors consider feature-comparison evidence a convincing
indicator of guilt, the provision of an evidentiary instruction has the potential to educate jurors
about the limitations of such evidence.
Keywords
decision making, evidence comprehension, evidentiary instruction, feature comparison,
forensic science, juries, scientific evidence
Corresponding author:
Eva Ribbers, Department of Psychology, University of Portsmouth, King Henry Building, King Henry 1 Street, Portsmouth, PO1
2DY, Hampshire, UK.
E-mail: eva.ribbers@myport.ac.uk
The International Journalof
Evidence & Proof
2018, Vol. 22(3) 262–288
ªThe Author(s) 2018
Article reuse guidelines:
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DOI: 10.1177/1365712718783427
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Introduction
England and Wales adhere to a procedural tradition of adversarial fact-finding and narrative building in
which the prosecution and defence are expected to collect evidence in the pre-trial phase to subsequently
present these findings in court (Brants and Field, 2016). Within this framework of adversarial litigation
jurors are considered impartial decision-makers who decide on innocence or guilt after an adequate
evaluation and discussion of the evidence (Brants and Field, 2016; Dunne, 2015). Criminal case judg-
ment in England and Wales is thus strongly wedded to the principle of lay fact-finding by jurors, who are
expected to employ common-sense reasoning in their assessment of the facts of the case (Jackson et al.,
2015).
With the increased popularity and compl exity of forensic evidence in court co mes the question
whether jurors are equipped with sufficient tools to carry out this responsibility. Legal reviews of past
convictions have given rise to an increased scepticism about the scientific basis of forensic evidence and
have put a spotlight on the occurrence of miscarriages of justice due to misconceptions regarding its
reliability (Adam, 2016). The discovery of a single piece of evidence during a criminal investigation can
become of crucial importance in court, an d the collection and analysis of evidenc e have therefore
become one of the most important and challenging features of the practice of law (Anderson et al.,
2005). This article investigates mock jurors’ assessment of forensic evidence through a literature review
and a mock jury experiment in which the impact of evidentiary instructions on decision-making in cases
with central and peripheral feature-comparison evidence is examined.
Scientific evidence
Forensic science refers to all scientific tests or techniques relevant to legal proceedings. The term masks
the complexities that come with the use of forensic science in court as a significant amount of such
evidence may come from disciplines outside of what has traditionally been understood as the forensic
sciences and can be produced by institutions and individuals whose primary discipline is unrelated to the
criminal justice system (e.g. expert medical testimony in Sudden Infant Death Syndrome cases) (Sense
about Science, 2017; Wilson et al., 2014). Due to this disciplinary fragmentation little attention has been
paid to underlying issues such as the potential of replication, confirmation through peer review or the
risks associated with bias, let alone to the difficulties that come with communicating scientific knowl-
edge to a lay audience (Dror et al., 2017; Jackson et al., 2015).
The increased concentration of expertise within the police effectively limits the availability of
equivalent experts to the defence, whose independent examination of the evidence may at times be the
only effective way of resolving bias (Wilson et al., 2014). In some fields of expertise it is in fact
impossible for a defence expert to obtain domestically recognised qualifications (Wilson et al., 2014).
For example, in RvSmith [2011] EWCA Crim 1296, the court expressed concern about the fact that
there is no opportunity to become qualified as a fingerprint expert in England and Wales except through
participation in the police force training. It then seems that the equality of arms on which adversarial
fact-finding is thought to depend may not exist in a system in which the prosecution has superior access
to witnesses, surveillance materials, forensic science support and databases (Brants and Field, 2016;
Wilson et al., 2014). The result of such inequality is that a judge may be more likely to accept evidence
provided by a prosecution expert, even though the context is one in which the expert pool available to the
defence is deficient (Wilson et al., 2014).
The closure of the Forensic Science Service (FSS) in 2012 is believed to have destabilised and even
posed a threat to the production of scientific evidence (Wilson et al., 2014). The lack of a common form
of governance regulating the forensic sciences has compromised the ability of judges and lawyers to
recognise problems with scientific evidence and to improve mechanisms for admitting, representing and
reviewing such evidence (Martire and Edmond, 2017; Roach, 2009). Consequentially, courts may rely
on simplistic or even misguided proxies for the evaluation and admission of such evidence while judges
Ribbers and Henneberg 263
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