New Zealand Law Society

Navigation menu

Research tests jury reasoning in institutional child sexual abuse trials

21 June 2016

There is neglible support for the notion that joint trials of alleged child sexual abusers with cross-admissible tendency evidence produce verdicts based on inter-base conflation of the evidence, character prejudice or accumulation prejudice.

This is one of the findings of research conducted within the Australian Royal Commission into Institutional Response to Child Sexual Abuse.

The Royal Commission, instituted in January 2013, is carrying out a comprehensive research programme to support its work and address the Terms of Reference.

The report Jury reasoning in joint and separate trials of institutional child sexual abuse: An empirical study has been carried out to assist the Government Responses research stream. Its authors are Professor Jane Goodman-Delahunty, Professor Annie Cossins and Natalie Martschuk.

The research investigated the extent to which joint trials with cross-admissible tendency evidence infringed defendants' rights, and the extent to which joint trials posed a risk of unfair prejudice to the defendant.

The researchers investigated the reasoning process of juries in a simulated joint trial of sex offences involving three complainants versus a separate trial involving a single complainant.

This involved presenting 10 different versions of a videotaped trial involving the same core evidence to a total of 1,029 jury-eligible mock jurors. The study tested the impact of evidence strength, the number of charges and the presence of specific judicial directions on jury decision-making in joint versus separate trials.

The researchers say they did not identify a joinder effect.

"As more inculpatory evidence against the defendant was added to the trials, conviction rates for both non-penetrative and penetrative offences against the focal complainant increased. Conviction rates in separate trials with relationship evidence and tendency evidence were significantly higher than those in the basic separate trial. However, there were no significant differences between conviction rates in the tendency evidence trial compared to the joint trial."

A quantitative analysis of the content of jury deliberations in which all statements that might indicate unfair prejudice against the defendant were coded revealed that impermissible reasoning was rare.

"And when it might have occurred, it was more likely in the separate trials without tendency evidence than in the trials with tendency evidence," the report says.

"We found a low rate of factual errors in jury deliberations; only 7.7% of juries made more than two factual errors. Two or more factual errors were more likely to occur in jury deliberations about the joint trial; that is, the trial with the most complex evidence. When errors were made, the vast majority were corrected in the course of deliberations, demonstrating the ability of jury groups to self-correct. None of the 90 jury verdicts were based on inter-case conflation of the evidence."

Summarising their most significant findings, the researchers say there was little indication that mock juries were susceptible to any joinder effect.

"Even if there was a joinder effect, there was no evidence that jury conviction rates were the result of impermissible propensity reasoning resulting in unfair prejudice to the defendant."

Last updated on the 16th September 2019