Factoring the Role of Eyewitness Evidence in the Courtroom

A pressing concern with the eyewitness testimony used in many criminal cases is that jurors may be swayed by the high confidence of an eyewitness and, as a result, may disregard other factors that provide more diagnostic information. Mock jurors were surveyed using a large national sample of 1,684 laypeople, selected to be representative of the U.S. population (age, race, gender, geographic region), using mock trial videos of eyewitness testimony. To explore the relationship between courtroom confidence and other factors, we used a fractional factorial design, permitting examination of the relationships among seven factors. Among these seven factors, we found that jurors gave most weight to the confidence of eyewitnesses, especially that expressed in the courtroom, irrespective of the eyewitness's testimony about confidence (low or high) at the initial police lineup. Jurors' assessments were not sensitive to the other factors or their interactions in the experiment: crime type (burglary or sexual assault), the race of the defendant and eyewitness, or information provided in judicial instructions or by expert testimony. The disproportionate importance of the eyewitness's expressed confidence has implications for the effectiveness of legal efforts to inform jurors about factors affecting eyewitness memory.