The Joint Effect of Scientific Knowledge and Photographic Evidence on Expert Witness Credibility

Abstract

The present study examines the role of scientific and photographic evidence on mock jurors’ perceptions of witness credibility and whether adding such details to an expert witness’s slideshow increases the credibility of that testimony. To assess credibility, 128 undergraduate students were divided across 4 research groups. The students reviewed narrated slideshows of Human Factors expert witness testimony and used the Witness Credibility Scale (Brodsky et al., 2010) to quantify the credibility of that testimony. We hypothesized that adding scientific data and photographs would lead to an increase in perceived credibility. Final results indicate that scientific data did generate a statistically significant increase in perceived credibility, specifically concerning the knowledge and trustworthiness of the witness. Conversely, the inclusion of images did not produce a statistically significant effect on perceived credibility. The results of this study demonstrate that including specialized scientific information in an expert witness’s testimony affects jurors’ overall perception of credibility of the witness.