Should Police Lineups Be Sequential or Simultaneous?

New analyses have rekindled debate over how lineups should be shown to witnesses

Posted Jun 25, 2014

This is a guest post by Daniel Loughran, Williams College Class of 2015.

Steve Titus was in the prime of his life: a successful Seattle businessman about to marry the love of his life, Gretchen. On October 12, 1980, Steve and his fiancé decided to treat themselves to a romantic dinner. On that same night, across the city, an unnamed seventeen year old female hitchhiker reported to the police a rape that had occurred around 6:45pm on a secluded road. The victim described the perpetrator as a 25-30 year old man with a beard, who drove a royal blue car with cloth seats and temporary license plates. Titus's Chevrolet Chevette resembled the rapists’ car and he vaguely resembled the rapist. He was arrested that night and booked on charges of rape.

When the rape victim was shown a photo line-up, she chose Steve Titus because his picture most resembled her attacker. By the time the trial started, the victim had spent a great deal of time thinking about the man who raped her. Because of the lineup, she saw Titus's face when she thought back to that night. All of this rumination created a false memory so powerful that she was positive Titus was the man who had committed this horrible crime.

Titus was convicted of rape. His family screamed at the jury and his fiancé collapsed to the floor, sobbing as Titus was taken to jail. The justice system failed Steve Titus. Equally as important, the rapist was still at large.

Was this injustice a freak occurrence? Unfortunately, no. It is all too common for crime victims to develop false memories that lead to wrongful convictions. The Innocence Project is dedicating to exposing and righting such wrongs. The Innocence Project is a national litigation and public policy organization dedicated to exonerating wrongfully convicted people through DNA testing and reforming the criminal justice to prevent future injustice. Since it’s founding in 1992, it has used DNA evidence to exonerate over 300 wrongfully convicted peoples (Gronlund et al. 2014). In nearly 75 percent of these convictions, faulty eyewitness identification played a significant role (Gronlund et al. 2014).

In order to combat faulty IDs made by eyewitness, researchers have experimented with a novel line-up procedure. The two methods being analyzed are the "simultaneous" line-up, where the witness views all line up members at once and a "sequential" line-up, in which the witness views members one at a time without knowing the number to be viewed (Wells et al. 2014).

Using simultaneous lineups effectively reduces the rate of false identifications. However, it also lowers the rate of correct identifications. A debate is currently underway in psychology about which procedure we should favor given the circumstances.

One one side of the debate, Gary Wells evaluates eyewitness identification processes using Probative Value (Diagnosticity Ratio) which refers to the strength of relationship between the evidence presented (eyewitness testimony) and the argument presented (accusation of rape) (Wells et al. 2014).

On the other side, Gronlund et al. prefers Receiver Operating Characteristic Analysis (ROC), a method that measures discriminability, or the degree to which eyewitnesses can differentiate between the innocent and guilty (Gronlund et al. 2014). The ROC method hypothetically removes instances of low confidence, a system that is comparable to an actual court proceeding since juries are likely to disregard eyewitness identifications of low confidence (although not necessarily; even if a witness's confidence was initially low, he or she might have become convinced by the time the trial begins). It is important to note that the overarching debate lies in the methodology for determining a specific line-up procedure's true efficacy.

Wells contends that sequential line-ups have a superior probative value; that is, victims make eyewitness identifications that are more accurate. Many studies suggest that sequential line-ups have a significantly higher probative than do simultaneous line-ups. Gronlund et al. argue that the increase in probative value is merely due to the fact that sequential line-ups induce conservative responding, such that witnesses are instructed not to make an identification unless they are absolutely sure. But perhaps conservatism is a good thing in a system where you are innocent until proven guilty.

The downside of conservatism is it can mean guilty persons are set free more often. This concern can be allayed somewhat when one considers the fact that guilty individuals tend to have more evidence against them beyond what is provided by an eyewitness testimony. Therefore, the optimistic viewpoint is that a missed identification does not suggest a guilty person goes free but it does mean that an innocent person will not be incarcerated.

There are good arguments on both sides, however. Gronlund et al. hypothesize that the idea of “sequential superiority” is not relevant due to the context in which the findings were discovered. Therefore, Gronlund et al. set out to find a better way to weave through the data and do so with the ROC procedure. As previously stated, the ROC method focuses on discriminability, which Gronlund et al. argue is the superior statistic for analysis. There appears to be no significant difference when analyzing data from both simultaneous and sequential line-ups through ROC when discarding low confidence values. Moreover, in some cases, the ROC data favors simultaneous line-ups. Therefore, simultaneous line-ups should continue to be used because they have proven to be more effective than sequential when the low confidence identifications (which tend to be wrong) are eliminated. When this happens, there is a decrease in false identifications but not a decrease in correct identifications.

Although both researchers make excellent points regarding which statistical method is superior, there are still many uncertainties regarding which line-up method should be adopted. Perhaps, as Wells suggests, we should consider changing the status quo and ask: What if sequential line-ups were standard and we recently discovered the effects of simultaneous procedures? Would we immediately want to change systems? Or would it be best to leave sequential line-ups as the standard? In my opinion (remember this is a guest post by Daniel), in order to protect the liberties of the innocent and provide closure for the victim, a more conservative (sequential) approach which increases probative value is necessary. 

I ask the reader, what do you think is the most appropriate system? The basis of the justice system in the United States is “innocent until proven guilty.” It is imperative that our system, whether through line-ups or some future physiological tests, maximizes efficiency in identifying a guilty person. No one should end as Steve Titus did, who - although eventually exonerated - was so consumed by losing his job, fiancé and all his savings that he died of a stress-induced heart attack days before his civil law suit trial.

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Gronlund, S. D., Wixted, J. T., & Mickes, L. (2014). Evaluating Eyewitness Identification Procedures Using Receiver Operating Characteristic Analysis. Current Directions in Psychological Science, 23(1), 3-10. doi: 10.1177/0963721413498891

Loftus, E. (2013, June). Elizabeth Loftus: The Fiction of Memory. Video File http://

Wells, G. L. (2014). Eyewitness Identification: Probative Value, Criterion Shifts, and Policy Regarding the Sequential Lineup. Current Directions in Psychological Science, 23(1), 11-16. doi: 10.1177/0963721413504781

Wixted, J. T., Gronlund, S. D., & Mickes, L. (2014). Policy Regarding the Sequential Lineup Is Not Informed by Probative Value but Is Informed by Receiver Operating Characteristic Analysis. Current Directions in Psychological Science, 23(1), 17-18. doi: 10.1177/0963721413510934 (Gronlund, Wixted, & Mickes, 2014)

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