Wells and Olsen have identified 2 variables that can affect the likelihood of accurate identifications:
- System Variables - refers to the methods or systems employed to try to maximise correct identification.
- Pre-line-up Instructions - given to the witness, such as explaining that a suspect might not be present
- The physical characteristics of the 'distractors' - It is important that the non-suspects are not obviously different from the suspect or the suspect would stand out
It is possible to control system variables. For example, one study showed that if a warning was given that the suspect might not be present in the lineup, identifications were reduced by 40%. However, it only reduced innacurate identification where the suspect was present by 2%
Estimator variables are things that affect identification, that were present at the scene and include:
- Use of weapons - the presense of a weapon during an event can result in 'weapon focus' where the eye-witness may focus on the weapon rather than the face of the perpetrator and this will effect eye-witness identification
- Conditions at the time of the event - e.g. poor lighting, bad weather conditions etc
The witness sees all of the members of the line-up at the same time.
The use of simultaneous line-ups increases the risk of relative judgements where the eye-witness compare each member of the line up to each other and then choose the person who matches the original memory of the perpetrator the best.
The witness sees each member of the line up one at a time.
This type of line-up increases the chance of absolute judgements as the eye witness compares each person individually to the original memory of the perpetrator.
Steblay et al
In a meta-analysis of studies using a sequential identification line-up, Steblay et al. concluded that this type of line-up does significantly reduce the rate of false identifications when the real suspect is absent, compared with performance in the simultaneous identification line-up.
However, the author found a slight drop in correct identifications in the sequential identification line-up when the suspect was present.
Dunning and Stem
Dunning and Stem asked eye-witnesses to give a verbal description of the process that they used to come to the identification decision.
They found that eye-witnesses who used a process of elimination (relative comparisons) were significantly more likely to make a false identification than those who reported a more absolute judgement.