Dissertations, Theses, and Capstone Projects

Date of Degree

6-2014

Document Type

Dissertation

Degree Name

Ph.D.

Program

Psychology

Advisor

Deryn M. Strange

Subject Categories

Psychology

Keywords

Forensic science, Juror decision-making, Media

Abstract

The National Academy of Sciences (2009) concluded that with the exception of nuclear DNA, none of the forensic sciences has been scientifically validated. It is not clear, however, that people are aware of these deficiencies. Indeed, people tend to think quite highly of forensic science, and find it to be convincing trial evidence. It is not clear to what extent their erroneous beliefs about validity influence the weight given to such evidence, or how best to challenge these beliefs. In the present research, I examined people's beliefs about forensic science and how their beliefs influenced their evaluations of forensic evidence. I also investigated the most effective ways to challenge their beliefs either during the trial (i.e., via cross-examination) or prior to the trial (i.e., via the media).

In the first part of the project (Study 1), I investigated pretrial reliability beliefs, and the influence of DNA, fingerprint, toolmark, and bitemark evidence in a homicide trial. The evidence matched or did not match the defendant and was countered by non-substantive, expert-focused, or evidence-focused cross-examination. Forensic evidence was viewed as more reliable than non-forensic evidence, and reliability beliefs influenced people's perceptions of the evidence. Although participants had some awareness of the comparative reliability of different disciplines, they tended to give too much weight to less valid disciplines. Further, evidence that matched the defendant was viewed as higher quality than evidence that did not match. Although cross-examination made people more skeptical of the forensic evidence, it did not reduce guilty verdicts.

In the second part of the project, I investigated the effectiveness of fact-based (Study 2) or story-based (Study 3) media reports in challenging people's beliefs about the validity of bitemark evidence, and whether reading such reports could help them to evaluate forensic evidence more appropriately. I found that a report which used complex language and attacked bitemark evidence from several angles was the most effective fact-based report. An illustrative story by itself was ineffective, but when the story was supplemented with factual information, it appeared to be the more effective than facts presented alone. Possible implications of these findings are discussed.

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