Making sense of sequential lineups: An experimental and theoretical analysis of position effects

•Reform-minded researchers have long pushed for the sequential lineup procedure.•The sequential lineup was not (and is still not) well understood theoretically.•Nevertheless, it has been implemented by  ∼5000 US Police Departments.•Signal-detection-based ROC analyses reveal key flaws, such as large position effects.•We emphasize the importance of theoretical understanding prior to implementation.