Increasing Eyewitness Accuracy in the Lineup Procedure Is All in How You Ask the Question
Lining up suspects behind a one-way mirror and allowing eyewitnesses to choose which one is the real perpetrator is standard police procedure. Yet DNA evidence has repeatedly revealed the limitations of this technique: many prison inmates whose convictions hinged on eyewitness identification were later proven innocent by DNA testing.
Long before the beginnings of DNA analysis, psychologists Roy Malpass and Patricia Devine doubted eyewitness' accuracy in the lineup procedure. In a clever experiment, they staged a crime in the middle of a lecture, during which a male "vandal" (who was actually hired by the researchers) entered the lecture hall, exchanged heated words with the instructor, and knocked over a rack of machines. The audience was then asked to participate in a lineup to identify the vandal. Results showed that witnesses made more or less accurate identifications in the lineup procedure, depending on the instructions the researchers gave them. The differences between the two sets of instructions were subtle: one set implied that the witness had to choose between the suspects in the lineup, while the other set implied that the witness did not have to make a choice. The researchers also made their experiment more sophisticated by including the real "criminal" in the lineup only half the time.
When witnesses thought they had to choose, they more frequently damned the wrong suspect. When witnesses thought they did not have to choose, however, they rarely made false identifications. When it came to identifying the correct 'bad guy," witnesses who were not induced to choose were just as accurate as were subjects who were induced to choose. Malpass and Devine therefore concluded that simply telling witnesses that they don't have to choose one of the suspects in the lineup causes them to make fewer false identifications, and does not hinder witnesses' ability to make accurate identifications.
Although inaccurate eyewitness testimonies are a notorious source of injustice in the American legal system, they are still regarded as among the strongest forms of evidence. Malpass and Devine's research simultaneously pointed out problems with relying on this evidence and suggested a way to improve its quality.
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Stebley, N. M. (1997). Social influences in eyewitness recall: A meta-analytic review of line-up instruction effects. Law and Human Behavior, 21, 283-298.
Wells, G. L., & Olson, E.A. (2003). Eyewitness testimony. Annual Review of Psychology, 54, 277-295.
American Psychological Association, May 28, 2003