a b s t r a c tShowups -when a single suspect is presented to an eyewitness -are thought to be a more suggestive procedure than traditional lineups by the U.S. Supreme Court and social science researchers. The present experiment examined the impact of retention interval on showup identifications, because immediate showups might be no worse than, and perhaps even better than, a lineup conducted after a delay. Participants (N = 1584) viewed a mock-crime video and then were presented with a showup or a simultaneous lineup, either immediately or a 48 h delay. Receiver operating characteristic (ROC) analyses revealed that a showup never resulted in better identification accuracy than a lineup. We conclude with a discussion of whether showups should ever be used.

Showups (a one-person identification) were compared to both simultaneous and sequential lineups that varied in lineup fairness and the position of the suspect in the lineup. We reanalyzed data from a study by Gronlund, Carlson, Dailey, and Goodsell (2009), which included simultaneous and sequential lineups, and using the same stimuli and procedures, collected new data using showup identifications. Performance was compared using ROC analysis, which is superior to traditional measures such as correct and false identification rates, and probative value measures. ROC analysis showed that simultaneous lineups consistently produced more accurate identification evidence than showups, but sequential lineups were sometimes no more accurate than showups, and were never more accurate than simultaneous lineups. These results supported prior suppositions regarding the suggestiveness of showups, revealed a misconception about the superiority of sequential lineups, and demonstrated why eyewitness identification procedures need to be evaluated using ROC analyses.

According to the Diagnostic Feature-Detection (DFD) hypothesis, the presence of fillers that match the eyewitness's description of the perpetrator will boost discriminability beyond a showup, and very few fillers may suffice to produce the advantage.We tested this hypothesis by comparing showups with simultaneous lineups of size 3, 6, 9, and 12. Participants (N = 10,433) were randomly assigned to one of these conditions, as well as target-present (TP) versus target-absent (TA) lineup. As predicted by the DFD hypothesis, lineups were superior to showups, and there was no advantage with increased lineup size beyond a 3-member lineup. The confidenceaccuracy (CA) relationship held a similar pattern. The only effect of increased lineup size was a lower likelihood of choosing a suspect (guilty or innocent). We conclude that police should focus more on the quality rather than quantity of fillers. K E Y W O R D S diagnostic feature-detection hypothesis, eyewitness identification, lineup size, showups, simultaneous lineup

Researchers have argued that simultaneous lineups should follow the principle of propitious heterogeneity, based on the idea that if the fillers are too similar to the perpetrator even an eyewitness with a good memory could fail to correctly identify him. A similar prediction can be derived from the diagnostic feature-detection (DFD) hypothesis, such that discriminability will decrease if too few features are present that can distinguish between innocent and guilty suspects. Our first experiment tested these predictions by controlling similarity with artificial faces, and our second experiment utilized a more ecologically valid eyewitness identification paradigm. Our results support propitious heterogeneity and the DFD hypothesis by showing that: 1) as the facial features in lineups become increasingly homogenous, empirical discriminability decreases; and 2) lineups with description-matched fillers generally yield higher empirical discriminability than those with suspect-matched fillers. Electronic supplementary material The online version of this article (10.1186/s41235-019-0172-5) contains supplementary material, which is available to authorized users.

Many crimes occur in which a perpetrator has a distinctive facial feature, such as a tattoo or black eye, but few eyewitness identification (ID) studies have involved such a feature. We conducted an experiment to determine how eyewitness ID performance is impacted by a distinctive facial feature, and how police could deal with this issue. Participants (N = 4,218) studied a target face with or without a black eye, and later viewed a simultaneous photo lineup either containing the target or not. For those who saw a target with a black eye, this feature was either replicated among all lineup members or was removed. The black eye harmed empirical discriminability regardless of replication or removal, which did not differ. However, participants responded more conservatively when the black eye was removed, compared to replication. Lastly, immediate confidence was consistently indicative of accuracy.