A Test of Combi-Lineups: A Lineup Procedure for Multiple Perpetrator Cases in the Netherlands

Background: International best-practice guidelines for lineup administration typically address single perpetrator crimes; few guidelines exist for cases involving multiple perpetrators. In the Netherlands, lineups testing the possible presence of several perpetrators are administered in a single intermixed sequence. This combi-lineup has the advantage that the witness does not know how many people are in the lineup and that it is cognitively less demanding for witnesses. It may also enhance memory performance through cueing effects. Method: In a laboratory (N = 158) and an online experiment (N = 213), we compared identification performance and the confidence-accuracy relationship for combi-lineups versus separate standard lineups. Participants viewed a mock-theft video depicting two thieves, and completed lineup tests for both. They either made identification decisions from a 12-person combi-lineup or from two separate 6-person lineups. Results: Discriminability, confidence-accuracy characteristic curves, and Bayesian information gain curves as a function of target presence base rates were very similar across both procedures. Conclusion: These findings provide evidence that the combi-lineup leads to results very similar to those obtained with multiple, separate standard lineups.