Admissibility of Polygraph Evidence in Court - Some Empirical Findings

• NCJ Number: 72593
• Journal: Law and Human Behavior Volume: 4 Issue: 1/2 Dated: (1980) Pages: 117-131
• Author(s): A Cavoukian; R J Heslegrave
• Date Published: 1980
• Length: 15 pages
• Sponsoring Agency: Canada Solicitor General; University of Toronto
• Publication Format: Article
• Publication Type: Report (Study/Research)
• Language: English
• Country: United States of America

Annotation

Results are reported from research that examined whether polygraph evidence affects jury decisions, and if so, whether jurors 'blindly' accept such evidence, and whether the cautioning of jurors about the accuracy of polygraph tests reduces the effect of such evidence.

Abstract

Polygraph evidence is presently inadmissible in Canadian courts and many jurisdictions of the United States. One of the major reasons for its exclusion is the belief held by members of the judiciary that jurors would accept such evidence without question, due to its technical/scientific character. The issues of such blind acceptance were examined in two experiments which tested 400 visitors to the Ontario Science Center (Canada) under varying conditions, to determine the effects of the introduction of polygraph evidence on their decisions in hypothetical court cases. Both experiments showed that the inclusion of polygraph evidence indicating the innocence of the accused encouraged subjects to perceive the accused as significantly less guilty in terms of perceived-guilt ratings and verdicts. These results suggest that significant differences could arise between jurisdictions on the basis of the admissibility or inadmissibility of such evidence. Neither study found evidence for the 'blind' acceptance of polygraph evidence. A caution from the judge produced a small reduction in the effect of polygraph evidence in both studies. While shifts in the level of perceived guilt with the inclusion of polygraph evidence were statistically significant, they were not overwhelming. In neither study did the perception of guilt shift significantly close to the point on the scale labeled 'probably not guilty.' If further research replicates these findings, then jurisdictons in which polygraph evidence is presently excluded should reconsider the question of admissibility, based on the observed discretion of jurors in weighing such evidence. Tabular and graphic data, footnotes and 26 references are procvided.