Double-Blind Lineup Administration

Definition

When a photo or live lineup is administered to an eyewitness, it is common for the police officer administering the lineup to be aware of the suspect's identity. This type of lineup procedure is referred to as a single-blind lineup, because although the witness is blind to the suspect's identity, the administrator of the lineup is not. Psycholegal researchers have expressed concern that when lineups are implemented in this fashion, the administrator may consciously or unconsciously emit cues to the witness and influence the witness's choice. This possibility is problematic when the suspect in question is actually innocent, as the witness could be led to misidentify an innocent person. Therefore, researchers have suggested that the police implement a double-blind procedure, meaning that both the witness and the police officer administering the lineup are unaware of which lineup member is the suspect.

Origins of the Recommendation for Double-Blind Lineups

In 1996, the American Psychology-Law Society (AP-LS; Division 41 of the American Psychological Association) selected a group of eyewitness experts to review the scientific literature on eyewitnesses and make recommendations regarding the best procedures for constructing and conducting lineups and photo spreads. In this paper, the authors argue that lineups can be viewed as a research experiment in which the lineup administrator is akin to the experimenter. In this lineup-as-experiment analogy, the police have a hypothesis that they are testing (i.e., that the suspect is the perpetrator), and they create materials (lineups) with which to test their hypothesis. The lineup administrator then collects data to test the hypothesis by administering the lineup to the witness, finally interpreting the results obtained from the witness to see whether they support the hypothesis that the suspect is the perpetrator. This panel noted that as in other types of experiments, lineups in which the lineup administrator knows which lineup member is the suspect produce a test of the hypothesis that is susceptible to bias.

Although these potential biases may not occur in a conscious or deliberate manner, social-psychological research suggests that when experimenters knew the [Page 243]hypotheses of their studies they unconsciously influenced the participants' behavior. The earliest of these experiments, conducted by Rosenthal and colleagues, demonstrated that experimenters influenced the ability of rats that they thought were “maze smart” to maneuver a maze faster than rats that they thought were “maze stupid,” even though there were no intellectual differences between the two groups of rats. In a similar experiment conducted with students attending a public school, Rosenthal and colleagues administered an intelligence test to students and informed the teachers that not only would this test determine a child's IQ but it would also pinpoint students who had the potential to make above-average intellectual progress throughout the year. Before the next school year began, teachers were given the names of the “gifted” students. In reality, their test had no such predictive ability, and the names had been drawn randomly. The students were tested again, and those who had been identified as being able to achieve aboveaverage development showed a larger gain in IQ points, and teachers' ratings of these students stated that they were better behaved, more interested in learning, and friendlier than their peers.

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