This report forms part of the Royal Commission into Institutional Responses to Child Sexual Abuse’s research program in relation to criminal justice system’s response to child sexual abuse in institutional contexts.

This study 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. In particular, we investigated the reasoning processes of juries in a simulated joint trial of sex offences involving three complainants versus a separate trial involving a single complainant.

Our jury deliberation and reasoning study investigated these issues by 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 five key aims of the project were to:

1. document juries’ interpretation of cross-admissible evidence in a joint child sexual abuse trial, to determine the extent to which juries engage in impermissible reasoning regarding such evidence

2. compare the above decision-making processes with those of juries in a separate trial involving the same defendant

3. compare trial outcomes (acquittal, conviction or hung jury) in a joint versus separate trial involving the same defendant

4. examine the relationship between jurors’ misconceptions about child sexual abuse, jury deliberations and decisions, and trial outcomes

5. determine the effect of question trail use on juries’ reasoning and decisions.