The inclusion of known-innocent fillers in a lineup is fairer than presenting only the suspect to an eyewitness and offers protection from mistaken identification if the suspect is innocent. This meta-analysis addresses the question of how many fillers should be included in a lineup. Data from 17,088 participants across 14 experiments revealed a trade-off associated with increasing the number of lineup members. Innocent suspects receive better protection from larger lineups than from smaller lineups, but larger lineups also make it harder for eyewitnesses to identify guilty suspects. Expected cost analyses showed that the least costly lineup size depends on the base rate of suspect guilt and the cost of incriminating an innocent suspect. If incriminating an innocent suspect is considered 10 times as costly as failing to incriminate the true perpetrator (Blackstone ratio), then larger lineups would be less costly for the majority of possible base rates. Smaller lineups would only be less costly if the base rate of suspect guilt is high, or if incriminating an innocent suspect is considered to have minimal costs. There remains much to learn about lineup size and its potential interactions with filler plausibility and the method of lineup presentation. Nevertheless, these preliminary results suggest that many jurisdictions would benefit from increasing the minimum number of fillers in their lineups.
- eyewitness identification
- lineup size