Published: 29 March 2014 at 15:15
Study investigates impact of bias and jurors' perceptions of beyond reasonable doubt
New research shows that the attitudes of jurors ahead of a trial have a significant impact on the verdict they are likely to deliver in court.
The study, published today in the British Psychological Society's Legal and Criminological Psychology journal, found that jurors with a pro-prosecution bias are more likely, given the same evidence, to find the defendant guilty than those with a pro-defence attitude.
The researchers hope that the methods used in their study can be adapted to help identify pre-trial bias and jurors who fail to understand the concept of beyond reasonable doubt.
The 1986 Contempt of Court Act in the United Kingdom prohibits the study of jurors sitting on real cases. Therefore, Dr Samantha Lundrigan (Senior Lecturer in Criminology at Anglia Ruskin University - pictured) and colleagues from the University of Cambridge and the University of Middlesex sampled a group of 118 people (aged between 19-63) employed by a large pharmaceutical company in Cambridge.
Participants were asked to imagine they were serving on a jury in a criminal trial. They read a trial summary of a fictitious burglary case, including details of the charge, background information (description of the dwelling, movements of the owners prior to discovery of the burglary and witness accounts), the prosecution and defence cases, and the judge's legal instructions on the presumption of innocence.
In relation to interpretations of the criminal standard of proof (beyond reasonable doubt), the study found that the average threshold required to find someone guilty was a probability of 95%.
The study also found that pre-trial attitudes combined with interpretations of beyond reasonable doubt accounted for 37% of the variability in the verdicts, so are an important predictor of how a juror will vote regardless of the evidence.
Dr Lundrigan, one of the research authors, said: "The results of our study show that jurors' judgments of innocence or guilt are associated with their pre-trial attitudes, as well as their interpretation of beyond reasonable doubt.
"For example, a juror with a pro-prosecution bias would be expected to have a lower conviction threshold, and a less stringent interpretation of beyond reasonable doubt, than a juror with a pro-defence bias. Consequently, the former would be more likely to return a guilty verdict than the latter."
Although UK courts don't allow jury selection, Dr Lundrigan believes that the tests used in the experiment could be adapted to highlight potential issues with jurors before trials begin. The judge or clerk of the court could assist these jurors by clarifying difficult concepts and explaining the importance of focusing solely on the evidence presented before them.
She added: "In jurisdictions where jury selection is permissible, such as the US, legal representatives are interested in identifying juror characteristics or attitudes that might signify sympathy towards their position. In the UK it is possible, although uncommon, for lawyers to challenge individual jurors and request that a juror 'stand by'.
"However, in both situations, legal representatives typically employ their own methods when making juror selection decisions, which may not be valid. Instead, pre-trial attitude questionnaires, such as those used in this study, could be used to ensure the juror has an appropriate interpretation of the standard of proof.
"Although public confidence in the British jury system is consistently high, it is vital to ensure that juries make their decisions by following legal rules. The fact that jurors might be biased by their pre-trial attitudes and inappropriate interpretations of beyond reasonable doubt suggests that initiatives are needed to deal with these issues."