The not-sure response option in sequential lineup practice

Field implementation of double-blind sequential lineups has prompted a question about the impact on eyewitness decisions of an explicit not-sure response option. In this laboratory study, a video crime was viewed by 378 participants who then attempted to identify the culprit from a six-person sequential or simultaneous-format lineup that either included or did not include the culprit. Witnesses were provided either dichotomous forced-choice (FC) response categories (yes/no) or a not-sure option as one of three response categories (yes/no/not-sure). The not-sure option (NSO) significantly decreased witness choosing compared to the FC condition but only for sequential lineups. Both correct identifications and false alarms decreased. Diagnosticity was greatest for a sequential lineup with a NSO. The results suggest a criterion decision shift for witnesses who view a sequential lineup with a not-sure response option. Copyright © 2010 John Wiley & Sons, Ltd.