Decision-Making Processes in Joined Criminal Trials

In Study 1, representative juror subjects viewed a realistic videotaped trial containing the same 'target offense' either tried by itself or in a joined trial of three offenses that varied as a function of (a) charge similarity, (b) evidence similarity, and (c) judges' instructions designed to reduce judgment biases. Subjects provided individual verdicts, deliberated in groups of six and reached a group verdict, and responded to a questionnaire that assessed processing of trial information. The results indicated that a defendant was more likely to be convicted on a particular charge in a joined trial than on the same charge tried by itself, and judges' instructions were totally ineffective at reducing judgment biases. Joinder led to confusion of evidence and negative inferences about the defendant. Study 2 replicated and extended the findings of Study 1 using nondeliberating undergraduates. The results of both studies suggest that increased convictions in joined trials are mediated through inferences about the defendant's criminality. (Author abstract)