Fair Lineups Improve Outside Observers’ Discriminability, Not Eyewitnesses’ Discriminability: Evidence for Differential Filler-Siphoning Using Empirical Data and the WITNESS Computer-Simulation Architecture

Fair lineups (good fillers) better sort between innocent and guilty-suspect identifications than do biased lineups (poor fillers). Why are fair lineups better? Some authors have suggested that the fair-lineup advantage is the result of an improvement in eyewitness discriminability. Others argue that the fair lineups do not improve eyewitnesses’ discriminability at all but instead improve the discriminability of outside observers who are privy to which lineup members are known-fillers (the differential filler-siphoning mechanism). Experiment 1 used a forced-choice paradigm to show that fair lineups do not improve eyewitness discriminability. Experiment 2 used the WITNESS computer-simulation architecture to show that differential filler-siphoning and the fair-lineup advantage readily surfaces and nicely patterns experimental data based on minimal assumptions even though fair lineups did not improve eyewitness discriminability.