Presumption Instructions and Juror Decision Making

Examined the effects of 3 types (conclusive, mandatory, permissive) of presumptions (“PRs”) on verdicts in a 4 (defendant culpability) by 6 (PR instruction) factorial design. 264 undergraduates read a case summary and completed a questionnaire about the summary. Only the conclusive PR significantly increased overall guilty verdicts. Additional analyses indicated that as defendant culpability decreased there was a greater tendency to nullify the PR instructions. The mandatory PR instruction intended to shift the burden of production elicited the most misapplications of the PR instructions (guilty verdicts that are inconsistent with the PR instruction)