Graduation Year


Document Type

Campus Only Senior Thesis

Degree Name

Bachelor of Arts



Second Department

Legal Studies

Reader 1

Jennifer Groscup

Reader 2

Jennifer Ma

Rights Information

© 2018 Kylie J Au


The “beyond a reasonable doubt” standard has long been a point of contention with regard to juror understanding of the American standard. Some legal authorities claim it to be intuitive, such that explicit explanation is unnecessary. Past research, however, reveals it as anything but. To represent the ambiguous standard, Justice Blackmun of the Supreme Court and numerous judges have endorsed the numerical foundation of 91%, such that juror confidence in the defendant’s guilt exceeds this value. Thus, the following study explored the effect of this quantitative instruction compared to the existing legal (qualitative) instruction on reasonable doubt comprehension and application. The veracity of the presumption of innocence within the reasonable doubt framework was also challenged. In this study, participants (N = 704) were given a vignette describing an armed robbery and asked to render a verdict based varying reasonable doubt standards of proof. A 2 (instruction framework: qualitative vs. quantitative) x 2 (instruction presumption: innocence vs. guilt) between groups factorial design was used to represent variations of the reasonable doubt instruction. Results indicate that the numerical anchor found in quantitative instructions did not yield a more consistent understanding and application of the reasonable doubt standard than the qualitative instruction. The results also imply that the presumption of innocence within reasonable doubt is flawed, and may be inherently guilt-presumptive. Implications on the reasonable doubt standard of proof in theory and in court are discussed.

This thesis is restricted to the Claremont Colleges current faculty, students, and staff.