The Admissibility of Polygraph Evidence in Court: Some Empirical Findings

Polygraph evidence is presently inadmissible in Canada and many jurisdictions of the United States. One of the major reasons for its exclusion lies in the belief (held by members of the judiciary) that jurors would accept such evidence without question due to its technical/scientific nature, The question of such blind acceptance was examined in two experiments on the influence of polygraph evidence on people's judgements of guilt. A second question that was also raised was whether a caution on the limitations of the polygraph would be effective in reducing people's weighting of such evidence. Although polygraph evidence was expected to exert some influence over judgements of guilt, it was not expected to be so great as to result in "blind acceptance." The results of both experiments supported this hypothesis. The inclusion of a caution was also effective in reducing the influence of such evidence. The implications of these findings are discussed in the context of the need to reexamine the admissibility of polygraph evidence in a court of law.