ESTIMATOR VARIABLES
While system variables can be controlled by our
justice system, estimator variables cannot. Essentially, estimator variables
are conditions that occur at the time of an incident that can, in some way, affect the witness’ ability to correctly identify a suspect (Wells, Memon,
& Penrod, 2006). Researchers have found that some of the most common and
significant estimator variables include: stress, cross-race identification,
exposure duration, alcohol, weapon focus, and retention interval (Wells et al.,
2006).
Stress
There have been numerous studies conducted on the effects of stress on eye-witness identification. Researchers have conducted a meta-analysis, a study of the studies, on a total of 63 tests and came to some conclusions about how stress affects witnesses (Wells et al., 2006). They concluded that subjects under high amounts of stress performed significantly worse in eye-witness identification than subjects under a low amount of stress (Wells et al., 2006). What this tells us is that when high levels of stress are introduced, witnesses are less likely to pick out the correct suspect.
Cross Race Identification
Research has shown that people have a hard time identifying people of another race. In many cases of mistaken identity, the victim is a different race than the suspect. Meissner and Bringham conducted a study that confirmed that people are 1.56 times more likely to mistakenly identify someone of a different race (Wells et al., 2006). They also found that participants were able to distinguish and categorize faces within their own race 2.2 times better than other-race faces (Wells et al., 2006). Pezdak, Blandon-Gitlin, and Moore conducted a study on younger people that ranged from kindergarten students to young adults. They found similar findings in that the subjects of the test were far less likely to identify someone of a different race than someone of their own (Wells et al., 2006). These studies show that the victim-suspect racial combination may have a significant effect on the accuracy of eye witness identification.
Witness Intoxication
There is a well-documented connection between alcohol consumption and diminished metal capability. Many people know the pain of waking up in the morning after a long night of drinking and not recalling anything about the night before. Most people would automatically assume that intoxicated witnesses would be far less likely to identify suspects correctly than sober people. Research has shown that intoxicated witnesses are in fact 30% more likely to wrongfully accuse someone in a target-absent situation than sober witnesses (Wells et al., 2006). However, they have found little differences in relation to target-present situations between the two sets of witnesses (Wells et al., 2006). Therefore, law enforcement must be very cautious when using intoxicated eye-witnesses.
Weapon Focus
Weapon focus is a term used to describe situations where witnesses are so focused on the weapon a suspect has, that they are unable to focus on the suspect themselves and their physical features (Wells et al., 2006). Researchers have conducted a meta-analysis of 19 studies involving 2,082 participants and that weapon focus can be a factor in misidentification (Wells et al., 2006). The researchers found that weapon focus had a minimal effect on the ability of witnesses to identify suspects and had somewhat larger effect on the ability of witnesses to accurately describe features of suspects (Wells et al., 2006). What this tells us is that the presence of a weapon can, in fact, limit the memory of a witness, but only to a degree.
Retention Interval
As all things eventually do, memory fades. In many cases our memories become less and less vivid as time goes by. Today, you can probably remember what you had for lunch yesterday. But can you remember what you had a week ago? In time we forget details. Shapiro and Penrod conducted a study to test how accurate witness identification is after a passage of time. As you might expect, they found that as the amount of time between the event and the actual identification increased, witnesses were less likely to correctly identify the suspect (Wells et al., 2006). It can then be gathered from this study that the sooner law enforcement officers are able to get a witness to identify a suspect, the more accurate they will be.
Exposure Duration
Exposure duration is the amount of time a witness is exposed to a suspect, specifically the facial features of a suspect that might be able to identify them. Memon, Hope, and Bull conducted a study to find what effects exposure duration had on the accuracy of suspect selection (Memon et al., 2003). They found some interesting facts. They found that the longer a witness was exposed to a crime, the more confident they were in selecting a person as the suspect (Memon et al., 2003). They found that subjects that were exposed to the crime longer had a higher success rate in identifying the suspect when the suspect was present in the lineup (Memon et al., 2003). However, they also found that those exposed to the crime longer also had a high level of incorrect selections when the target was not present (Memon et al., 2003). What they found was that high levels of exposure can increase the abilities of the witnesses to accurately identify subjects when they are present. However, the inflated confidence they gained from seeing the suspect for so long, led them to being highly confident in an incorrect choice. This study showed that there is no correlation between high confidence and accuracy (Memon et al., 2003). Juries and law enforcement professionals should take from this that just because someone is highly confident in whom they pick out in a lineup, they should not necessarily jump to the conclusion that they got the right person.
References
Wells, G. L., Memon, A., & Penrod, S. (2006). Eyewitness evidence: Improving its probative value. Psychological Science in the Public Interest. 7(2), 45-75.
Memon, A., Hope, L., & Bull, R. (2003). Exposure duration: Effects on eyewitness accuracy and confidence. British Journal of Psychology. 94, 339-354.
Stress
There have been numerous studies conducted on the effects of stress on eye-witness identification. Researchers have conducted a meta-analysis, a study of the studies, on a total of 63 tests and came to some conclusions about how stress affects witnesses (Wells et al., 2006). They concluded that subjects under high amounts of stress performed significantly worse in eye-witness identification than subjects under a low amount of stress (Wells et al., 2006). What this tells us is that when high levels of stress are introduced, witnesses are less likely to pick out the correct suspect.
Cross Race Identification
Research has shown that people have a hard time identifying people of another race. In many cases of mistaken identity, the victim is a different race than the suspect. Meissner and Bringham conducted a study that confirmed that people are 1.56 times more likely to mistakenly identify someone of a different race (Wells et al., 2006). They also found that participants were able to distinguish and categorize faces within their own race 2.2 times better than other-race faces (Wells et al., 2006). Pezdak, Blandon-Gitlin, and Moore conducted a study on younger people that ranged from kindergarten students to young adults. They found similar findings in that the subjects of the test were far less likely to identify someone of a different race than someone of their own (Wells et al., 2006). These studies show that the victim-suspect racial combination may have a significant effect on the accuracy of eye witness identification.
Witness Intoxication
There is a well-documented connection between alcohol consumption and diminished metal capability. Many people know the pain of waking up in the morning after a long night of drinking and not recalling anything about the night before. Most people would automatically assume that intoxicated witnesses would be far less likely to identify suspects correctly than sober people. Research has shown that intoxicated witnesses are in fact 30% more likely to wrongfully accuse someone in a target-absent situation than sober witnesses (Wells et al., 2006). However, they have found little differences in relation to target-present situations between the two sets of witnesses (Wells et al., 2006). Therefore, law enforcement must be very cautious when using intoxicated eye-witnesses.
Weapon Focus
Weapon focus is a term used to describe situations where witnesses are so focused on the weapon a suspect has, that they are unable to focus on the suspect themselves and their physical features (Wells et al., 2006). Researchers have conducted a meta-analysis of 19 studies involving 2,082 participants and that weapon focus can be a factor in misidentification (Wells et al., 2006). The researchers found that weapon focus had a minimal effect on the ability of witnesses to identify suspects and had somewhat larger effect on the ability of witnesses to accurately describe features of suspects (Wells et al., 2006). What this tells us is that the presence of a weapon can, in fact, limit the memory of a witness, but only to a degree.
Retention Interval
As all things eventually do, memory fades. In many cases our memories become less and less vivid as time goes by. Today, you can probably remember what you had for lunch yesterday. But can you remember what you had a week ago? In time we forget details. Shapiro and Penrod conducted a study to test how accurate witness identification is after a passage of time. As you might expect, they found that as the amount of time between the event and the actual identification increased, witnesses were less likely to correctly identify the suspect (Wells et al., 2006). It can then be gathered from this study that the sooner law enforcement officers are able to get a witness to identify a suspect, the more accurate they will be.
Exposure Duration
Exposure duration is the amount of time a witness is exposed to a suspect, specifically the facial features of a suspect that might be able to identify them. Memon, Hope, and Bull conducted a study to find what effects exposure duration had on the accuracy of suspect selection (Memon et al., 2003). They found some interesting facts. They found that the longer a witness was exposed to a crime, the more confident they were in selecting a person as the suspect (Memon et al., 2003). They found that subjects that were exposed to the crime longer had a higher success rate in identifying the suspect when the suspect was present in the lineup (Memon et al., 2003). However, they also found that those exposed to the crime longer also had a high level of incorrect selections when the target was not present (Memon et al., 2003). What they found was that high levels of exposure can increase the abilities of the witnesses to accurately identify subjects when they are present. However, the inflated confidence they gained from seeing the suspect for so long, led them to being highly confident in an incorrect choice. This study showed that there is no correlation between high confidence and accuracy (Memon et al., 2003). Juries and law enforcement professionals should take from this that just because someone is highly confident in whom they pick out in a lineup, they should not necessarily jump to the conclusion that they got the right person.
References
Wells, G. L., Memon, A., & Penrod, S. (2006). Eyewitness evidence: Improving its probative value. Psychological Science in the Public Interest. 7(2), 45-75.
Memon, A., Hope, L., & Bull, R. (2003). Exposure duration: Effects on eyewitness accuracy and confidence. British Journal of Psychology. 94, 339-354.