A double-blind lineup refers to a lineup procedure in which both the witness and the lineup administrator are unaware of which lineup member is the suspect under investigation. Scholars began recommending this procedure, in contrast to the typical procedure in which the lineup administrator knows which lineup member is the suspect, because of concerns that a nonblind administrator would unintentionally communicate to the witness the identity of the suspect, increasing the rate of mistaken identifications when the suspect is not the perpetrator. Laboratory research suggests that the use of double-blind lineups may decrease the rate of mistaken identifications, especially when other lineup procedures lead to an increase in identification rates.
Double-Blind Lineup 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 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 above-average 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.
This research paper has obvious implications for conducting lineups to test eyewitness memory. If a lineup administrator knows which lineup member is the suspect, he or she may consciously or unconsciously give verbal or behavioral cues to the witness that would influence the witness to choose the photo of the suspect. If the lineup administrator were blind to the suspect’s identity, however, it would eliminate these expectancy effects and result in an unbiased lineup administration. Furthermore, the use of double-blind lineup procedures could also eliminate the influence of postidentification feedback on witnesses’ ratings of their confidence in the accuracy of their identification decision.
At about the same time that the AP-LS group recommended double-blind lineups as a best practice in conducting lineups, the then U.S. attorney general Janet Reno convened a task force comprising psychologists, lawyers, judges, and police officers to create a manual of recommended best practices for police stations to follow when conducting an investigation. Although many of the practices suggested by the AP-LS group were also recommended in the manual, the task force did not include double-blind procedures in the guidelines for collecting eyewitness evidence. Instead, administrator knowledge of the suspect’s identity was addressed in the introduction to the manual, where police officers were instructed on the possible dangers of single-blind lineups. However, the authors stated that they had refrained from including double-blind procedures in the recommendations because police officers had expressed concerns about the logistics of implementation. For example, many police stations with small police forces might find it difficult to locate a police officer who was not aware of the suspect’s identity.
Empirical Support for the Use of Double-Blind Lineups
Psychological research specifically testing the influence of administrator knowledge has not produced a definitive answer as to whether single-blind lineups are more likely to result in mistaken identifications than are double-blind lineups. Early research seemed to indicate that when single-blind administrators presented a sequential lineup to a witness, the witness identified the innocent suspect in a target-absent lineup more often than when double-blind procedures were used, but only when there was a third party observing the lineup administration; there was no effect of investigator knowledge of the suspect’s identity for simultaneous lineups. Other research that manipulated administrator contact with an eyewitness found that administrators who were aware of the suspect’s identity and presented simultaneous lineups to an eyewitness produced more mistaken identifications than did administrators who were not allowed direct contact with a witness (instead presenting the witnesses with a folder containing the photographs and sitting behind the witnesses while they viewed the lineup photos). Several other studies have failed to find an effect of administrator influence at all. The most recent research on administrator influence has found that other biasing factors, such as biased instructions, need to be present for single-blind administrators to influence witnesses’ decisions. It has been hypothesized that these other biasing factors serve to lower witnesses’ criterion levels necessary to make an identification and, therefore, allow more opportunities for knowledgeable administrators to influence a witness.
- Phillips, M. R., McAuliff, B. D., Kovera, M. B., & Cutler, B. L. (1999). Double-blind photoarray administration as a safeguard against investigator bias. Journal of Applied Psychology, 84, 940-951.
- Rosenthal, R. (1966). Experimenter effects in behavioral research. New York: Appleton-Century-Crofts.
- Russano, M. B., Dickinson, J. J., Greathouse, S. M., & Kovera, M. B. (2006). Why don’t you take another look at number three: Investigator knowledge and its effects on eyewitness confidence and identification decisions. Cardozo Public Law, Policy, and Ethics Journal, 4, 355-379.
- Technical Working Group for Eyewitness Evidence. (2003). Eyewitness evidence: A trainer’s manual for law enforcement (NCJ 188678). Washington, DC: U.S. Department of Justice, National Institute of Justice.
- Wells, G. L., Small, M., Penrod, S., Malpass, R. S., Fulero, S. M., & Brimacombe, C. A. E. (1998). Eyewitness identification procedures: Recommendations for lineups and photospreads. Law and Human Behavior, 22, 603-647.