Some juror decisions are influenced by perceptions of the prevalence of crimes which can be incorrect or biased, a new study shows.

The research shows people hold diverse views about how often legally relevant events including sexual assaults and false allegations of sexual assaults take place, and these views differ based on gender and political beliefs.

For example, men believe that child sexual assault and psychological harm resulting from abuse are less prevalent than women do. These views are likely to feed into evaluations of complainant and defendant testimony and, ultimately into legal verdicts, highlighting the need for gender balance on juries.

As part of the University of Exeter study, published in the journal Applied Cognitive Psychology, 539 people aged between 37 and 61 were asked to estimate how common a set of legally relevant events were and to examine evidence in two hypothetical cases. One case involved an accusation of child sexual assault, and the other involved a defence to homicide based on domestic violence. Participants were asked to make judgments about complainant and defendant evidence in each case and to indicate how they would decide the case if they were on a jury.

Results showed participants of different genders and political beliefs evaluated evidence differently, and this difference was partly explained by different perceptions of how common underlying alleged events were. In the child sexual assault case, women were more likely to believe the victim and render a guilty verdict – an effect explained partly by the fact that women rated child sexual assault as being more prevalent than men did in the general population. 

Dr Rebecca Helm said: “Our results show that people hold very varied views about how prevalent legally important events are and that these opinions on prevalence can influence their legal judgments. This influence is important since views on prevalence can be biased, for example by personal experience, experiences of friends, or media coverage. When views on prevalence influence legal judgments they can create bias in those judgments.

“While the jury system specifically relies on jurors drawing on personal experience, this may be inappropriate where a juror’s experience base is drastically different from that of the people they are making judgements about. Unreasonable and uninformed views about relevant prevalence should be viewed in the same way as problematic beliefs such as rape myths– as damaging misconceptions to be corrected.”