The Effects of Polygraph Evidence and Eyewitness Testimony on the Beliefs and Decisions of Mock Jurors

Abstract

Mock jurors heard one of four versions of a murder trial and then deliberated in small groups to a verdict. Half the juries heard a trial in which an eyewitness identified the defendant as the murderer and half heard a trial in which a polygraph expert testified that the defendant responded deceptively when denying the crime. These two factors were completely crossed in a 2 × 2 (eyewitness/no eyewitness x polygraph/no polygraph) design. Jurors exposed to the eyewitness testimony believed more strongly in the defendant's guilt and voted guilty more frequently than did those not exposed to eyewitness testimony. Eyewitness testimony also enhanced the degree to which jurors believed that other pieces of evidence indicated that the defendant was guilty. Polygraph evidence exerted no significant effects either on jurors' beliefs or on their verdicts.

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