Decision making in joined criminal trials: The influence of charge similarity, evidence similarity, and limiting instructions.

The present research investigated decision-making processes in “joined” trials of multiple offenses. Subjects judged videotaped trials of three joined charges in a factorial design that varied charge similarity, evidence similarity, and judges' instructions designed to reduce judgement biases; or judged one of several charges presented individually. The results indicated that subjects were more likely to convict a defendant in a joined trial than on the same charge tried by itself, particularly when the charge was presented in the third position. Convictions were more frequent when joined charges were similar, and judges' instructions significantly reduced conviction rates. Subjects judging joined trials confused evidence among charges, rated the prosecution's evidence as stronger, and rated the defendent less favorably than subjects judging single trials. The findings were compared statistically to the results of previous research, and it was concluded that increased convictions in joined trials are robust effects.