In the previous chapters we talked about some of the most important variables that can influence the accuracy of eyewitness identification. In Chapter 3, we reviewed estimator variables-those variables that police have no control over that can influence eyewitness accuracy. In Chapter 4, we reviewed system variables-those variables that police have control over that can influence eyewitness accuracy. An important point about both types of variables is that they are best understood as being causal antecedents of eyewitness accuracy. For example, poor lighting causes eyewitness identification to suffer. Giving biased lineup instructions causes false identifications to increase.