The instructions given to a witness prior to the presentation of a lineup have an important influence on how the witness views the identification task and how the witness makes a decision whether to make an identification or whom to identify.
Biased Versus Unbiased Instructions
Because the suspect in the lineup may be innocent, it is important that police officers instruct the witnesses that the actual perpetrator may or may not be in the lineup and that they are not obligated to make an identification. Because these instructions are unbiased with respect to the presence or absence of the perpetrator, they are typically called unbiased instructions. In contrast, instructions that explicitly state or imply that the perpetrator is in the lineup and that the witness should make an identification are called biased instructions.
It is not surprising that biased instructions result in more identifications. Witnesses who are led to believe that the perpetrator is in the lineup and that it is their “job” to identify him or her make more identifications. The question, of course, is whether they make more correct identifications or more false identifications. As simple as the question is, it does not have a simple answer. Some studies have shown that biased instructions lead to increases in both correct and false identifications, and some studies show only increases in false identifications with little or no change in correct identifications.
The consistent increase in false identifications arises because biased instructions lead to more identifications, and if the perpetrator is not in the lineup (i.e., the suspect is innocent), then any identification made by the witness will be an error. The most critical errors, of course, are the false identifications of the innocent suspect. The proportion of identifications of the innocent suspect (rather than one of the foils—i.e., an innocent person in a police lineup) depends on the composition of the lineup.
The question remains: Is there variation in the outcomes for correct identifications? Some of the variation is likely due to ceiling effects. Considering only those lineups in which the perpetrator is present, if the identification rate is fairly high under unbiased instruction conditions, then it cannot increase very much under biased instruction conditions. Consequently, the correct identification rate cannot increase very much either.
However, the variability in correct identification rates cannot be explained by ceiling effects alone. Results showing an increase in the overall identification rate (when the perpetrator is in the lineup), with no increase in the correct identification rate, suggest that the biasing effect of the instructions is not simply to lower the witness’s decision criterion. Instead, in studies showing this pattern of results, the biasing instructions may induce witnesses to change their decision rule or change the way they compare the lineup members with their memory. Another explanation arises from the reasons why witnesses do not identify the perpetrator in the first place. If witnesses who are presented with a lineup that includes the perpetrator do not make any identification, it may be because their memories are quite distorted and inaccurate, such that if they are biased to make an identification, it is very likely that one of the lineup fillers will be a better match to their (distorted) memory of the perpetrator than the perpetrator himself (or herself).
Unbiased Instructions and Biased Lineup Administrators
Police officers may sometimes give witnesses a mixed message by reading an unbiased instruction but then follow that instruction with various encouragements and nudges, suggesting that they should make an identification and even who they should identify. Even seemingly innocuous comments to “take your time” or “look at each photograph carefully” can convey to witnesses that they should make, rather than not make, an identification. Other forms of prompting can direct witnesses as to whom to identify. The point here is that police officers can essentially “undo” their unbiased instructions with biased nudges and prompting.
The prompting may be explicit, or it may be quite inadvertent. Consider, for example, a police officer who knows that the suspect is in Position 4 and is quite certain that the suspect is the perpetrator. If the witness states, “Number 3 looks familiar,” should that be considered an identification of Number 3 or a case of the witness thinking out loud? Because the police officer knows that Number 3 is a filler, he or she may interpret the witness’s comment as thinking out loud and say something like “Take your time.” Because of such interpretation problems, it is recommended that the police officer administering the lineup be blind to the identity and position of the suspect in the lineup.
It is also common to instruct witnesses, prior to the presentation of a lineup, that people can change their appearance. The perpetrator, as pictured in a photograph, may have lost or gained weight, grown or shaved a beard, and so on. (A booking photograph used in a photo lineup may have been taken years before or years after the witnessed crime.)
What effect does this instruction have? There is considerably less research on the effects of the appearance-change instruction than the “may or may not be present” instruction. However, one study by Steve Charman and Gary Wells showed that the appearance-change instruction had only one effect— to increase false identifications. They suggested that the appearance-change instruction may function to make witnesses more lenient and to decrease their decision criterion. What has not been shown is that the appearance-change instruction serves its presumably intended purpose of increasing the likelihood of correct identifications of perpetrators who have, in fact, changed their appearance.
- Charman, S. D., & Wells, G. L. (in press). Eyewitness lineups. Is the appearance-change instruction a good idea? Law and Human Behavior.
- Clark, S. E. (2005). A re-examination of the effects of biased lineup instructions in eyewitness identification. Law and Human Behavior, 29, 395—124.
- Steblay, N. M. (1997). Social influence in eyewitness recall: A meta-analytic review of lineup instruction effects. Law and Human Behavior, 21, 283-297.