Gary L. Wells
Iowa State University
The hot question regarding simultaneous versus sequential lineups concerns the issue of whether there is a reduction of accurate identifications resulting from the sequential lineup. Although the reduction of mistaken identifications from the sequential lineup is well established and robust, some have been surprised to encounter the idea that accurate identification rates can also be lower with the sequential lineup than with the simultaneous lineup.
Some loss of accurate identifications resulting from the sequential lineup should not be surprising to those who understand the psychological mechanisms involved. This is because some of the "accurate identifications" that come from the simultaneous lineup are the result of mere relative judgments. In other words, some witnesses who have rather weak memories will nevertheless pick out the culprit because they are simply picking the person who looks most like the culprit compared to the other lineup members. These weak memory witnesses would not, however, be able to identify the culprit from a sequential lineup because they don't have a good enough memory to do anything but make the shallow relative decision. Furthermore, these same witnesses would be prone to misidentify someone from a simultaneous lineup if the culprit was not present. In a sense, these witnesses are guessing and happen to guess correctly. The sequential lineup largely eliminates this type of guessing and, therefore, there is some loss in hits.
The sequential-superiority effect can be defined as the ability of the sequential lineup to produce a higher overall ratio of accurate to mistaken identifications of suspects. In spite of some loss in accurate identifications, the sequential-superiority effect, as defined by the ratio of accurate to inaccurate identifications, holds up quite well.
The most complete data set was published recently by Steblay and colleagues. [Steblay, N. M., Deisert, J., Fulero, S. & Lindsay, R.C.L. (2001). Eyewitness accuracy rates in sequential and simultaneous lineup presentations: A meta-analytic comparison. Law and Human Behavior, 25, 459-474.] Their article is a meta-analysis of the 9 published and 13 unpublished papers on simultaneous versus sequential lineups and the data are based on 4,125 research participants. Below are the summary analyses that provide the pertinent overall statistics:
Correct identification rates of the culprit when the culprit is in the lineup are 50% for the simultaneous and 35% for the sequential. So, the sequential yields only 70% of the "hits" that the simultaneous does. [The actual differences are likely to be much smaller than this in actual cases for reasons outlined in the Steblay et al article in their conclusions section on page 471. However, I'll assume this magnitude difference in hit rates so as to deal with the "worst case scenario".]
Mistaken identification of an innocent "stand in" for the culprit is 27% for the simultaneous and 9% for the sequential. So, the sequential yields only 33% of the "false alarms" that the simultaneous yields.
A way to examine the overall results is to calculate the hit-to-false alarm ratio for identifications of the suspect for sequential compared to simultaneous lineups in these studies. The simultaneous yields a ratio of 50:27 or slightly under 2.0. The sequential yields a ratio of 35:9 or nearly 4.0. This means that one can trust the sequential lineup to yield odds of guilt from the identification of a suspect that are approximately twice that of the simultaneous lineup.
Although some policy makers have started to fret over the loss in accurate identifications that can result from the sequential lineup, it should be noted that the odds of an identification of the suspect being accurate are approximately doubled by the use of the sequential lineup in spite of some loss of accurate identifications. In addition, it seems clear that policy makers should not favor a particular method of conducting lineups merely because it yields more hits. Consider, for instance, a method in which witnesses who claim that they do not recognize anyone are told to guess instead. This guessing method would yield more hits than would a method that discouraged guessing, but surely policy makers would not want such a method used.
For more information on various issues regarding eyewitness
identification with an emphasis on how to improve the reliability of the
evidence, see the following links: