College of Graduate Studies: Theses & Dissertations

Term of Award

Spring 2026

Degree Name

Master of Science in Experimental Psychology (M.S.)

Document Type and Release Option

Thesis (open access)

Copyright Statement / License for Reuse

Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.

Department

Department of Psychology

Committee Chair

Amy Hackney

Committee Member 1

Michael Nielsen

Committee Member 2

Kristina Thompson

Abstract

Forensic science plays a critical role in criminal trials, yet forensic techniques vary in their reliability. Expert testimony, often held in high regard by jurors, can be a decisive factor in verdicts, but its influence is complicated by factors such as technical complexity, adversarial bias, and heuristic processing. The present study examined how the complexity of prosecution expert testimony and the presence of a defensive rebuttal influenced jurors’ decisions when presented with faulty forensic evidence. Participants (N = 142) were randomly assigned to one of four conditions in a 2 (testimony complexity: high v. low) x 2 (defensive rebuttal (present v. absent) between-subjects design. All participants were presented with trial testimony that included invalid expert testimony. Dependent measures included confidence in guilt, perceived credibility of the prosecution’s expert witness, and confidence in the prosecution’s evidence. It was hypothesized that participants exposed to faulty low-complexity testimony paired with a defensive rebuttal would be more likely to render a correct not guilty verdict, while participants exposed to high-complexity testimony without a defensive rebuttal would be more likely to render unjust guilty verdicts.  Results indicated that the presence of a defensive rebuttal significantly reduced confidence in guilt, perceived credibility of the prosecution’s expert, and confidence in the prosecution’s evidence. Contrary to predictions, the complexity of the expert testimony did not significantly affect confidence in guilt or perceived credibility of the prosecution’s expert; however, simpler expert testimony increased confidence in the prosecution’s evidence, opposing the predicted direction. These findings suggest that defensive rebuttals play an important role in promoting critical evaluation of forensic evidence, even when such evidence is presented with varying levels of complexity. The results have important implications for the legal system, particularly regarding disparities in access to expert witnesses and the potential for wrongful convictions when forensic testimony is not effectively challenged.

OCLC Number

1588479737

Research Data and Supplementary Material

No

Download

Share

COinS