Estimator variables are factors present at the time of an incident that can affect the accuracy of eyewitness identification but are outside the control of the criminal justice system. These variables include conditions such as stress, cross-race identification, exposure duration, alcohol influence, weapon focus, and retention interval. They influence how well a witness can correctly identify a suspect, with suboptimal estimator variables typically reducing the reliability of eyewitness identifications, especially when the confidence level of the identification is low.

In the context of eyewitness testimony, estimator variables contrast with system variables, which are aspects under the control of the justice system. Understanding estimator variables helps in assessing the potential accuracy of eyewitness identifications in legal contexts.