Predicting verdicts, adherence to judge's instructions, and assumptions about the disposition of the defendant in a case involving the insanity defense

Abstract

296 college students and jury eligible adults completed attitudinal measures and read a case summary of a murder trial involving the insanity defense. The case summary included opening and closing arguments, testimony from expert witnesses, and judge's instructions. Although broader legal attitudes (the PJAQ) predicted verdicts, the Insanity Defense Attitudes-Revised scale provided incremental predictive validity. Attitudes related to the insanity defense also predicted adherence to judge's instructions, whereas more general legal biases predicted a juror's willingness to change their verdict after being provided with accurate information about the defendant's disposition following the verdict. Importantly, misconceptions concerning the insanity defense impacted verdicts and many jurors made decisions that failed to adhere to the judge's instructions, though the nullification tendency does appear to vary as a function of pretrial juror attitudes. Implications for instructing jurors in insanity defense cases will be discussed.

Keywords:

• juror bias
• PJAQ
• IDA-R
• verdict change
• nullification

Acknowledgements

Portions of this manuscript were presented at the 2008 Annual convention of the American Psychological Association. This manuscript was based in part on the first author's master's thesis. Special thanks to Michael Peters for help with manuscript preparations.