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Current guidelines for selecting lineup fillers are imprecise. Consequently, filler characteristics likelyvary widely across lineups, potentially affecting identification decisions in important but unexplainedways. We report 2 experiments investigating the impact of 1 source of variation, the number of relativelyhigh versus low similarity match-description fillers, on identification outcomes. Identifications followinga retention interval of a few minutes (Experiments 1 and 2) and several weeks (Experiment 2) wereexamined. Increasing the number of high similarity lineup members within match-description lineupsincreased choosing (characterized by more filler but fewer suspect identifications), decreased accuracyand confidence and caused a poorer confidence-accuracy relationship. The changes to identificationoutcomes as the number of high similarity fillers increased were attributable to decreased discriminabilityand a relaxed criterion, with positive identifications requiring a lesser evidential discrepancy betweentarget and fillers. There was limited evidence of guilty and innocent suspect identifications beingdifferently affected by variations in the number of high similarity fillers and no evidence of suspectdiscriminability being influenced. For decisions after a short retention interval, high confidence suspectidentifications were good predictors of accuracy; however, high similarity match-description fillersundermined the predictive value of high confidence suspect identifications at the long retention interval.Our results suggest that future research must explore methods for curbing variation in identificationpatterns resulting from uncontrolled filler characteristics. Until then it is critical that identificationevidence be interpreted acknowledging that, even in lineups constructed following best practice guidelines, filler characteristics could have profoundly influenced the outcome.
Lucas et al. (Mon,) studied this question.