System Variables

System variables refer to factors that can influence identification accuracy that are under the control of law enforcement. In this present chapter, we discuss system variables that operate at the level of the identification procedure. The chapter covers topics of how fillers are selected for lineups, how witnesses are instructed, and whether the lineup is conducted in a double-blind fashion. We also discuss showups and compare and contrast them with lineups. The chapter also wades into the debate about sequential versus simultaneous lineups. Many scientific and law enforcement organizations have developed best practice recommendations for lineups and we discuss those as well.