Penrod and Cutler, (1995) ‘Witness Confidence and Witness Accuracy: Assessing their Forensic Relation’, Psychology, Public Policy and Law 1 (4), 817–45.
Background
This is the second study we will be looking at from the ‘witness appeal’ section of ‘reaching a verdict’, as part of your OCR A2 Forensic Psychology course. It is further categorised into ‘witness confidence.’
One of the most convincing features of a witness is their confidence when delivering their version of events.
Estimator and System Variables
Estimator variables: are variables which affect the accuracy of eyewitness identifications, but cannot be controlled by the criminal justice system e.g. during the acquisition phase, lighting, conditions, distance, arousal and the presence of weapons can all effect the witness.
System Variables: are variables which affect the accuracy of eyewitness identifications, but the criminal justice system can control those variables. System variables tend to revolve around factors involved in the retrieval phase, such the structure of a line up, instructions given to witnesses prior to viewing a line up and so on.
Aim
Penrod and Cutler (1995) aimed: to examine several factors including confidence that jurors might consider when evaluating eyewitness identification evidence.
Method and Design
A laboratory experiment of a mock trial.
Participants were randomly assigned using an independent measures design.
Participants
Undergraduates, eligible and experienced jurors.
Procedure
A videotaped trial of a robbery was shown in which eyewitness identification played a key role.
The witness testified that she was either 80% or 100% confident that she had correctly identified the robber.
There were nine other variables all at both high and low levels, depending on the conditions.
The participants experienced either the high or low condition variables on a random basis and were asked to decide whether the robber was guilty or not guilty after watching the film.
Findings
Percentages refer to the percentage of convictions.
Suspect in disguise
High – heavily disguised 63%
Low – minimal disguise 63%
Weapon Focus – a weapon is used
High – weapon clearly brandished 64%
Low – Weapon visible 63%
Retention Interval
14 days – 63%
2 days – 63%
Witness Confidence about identification
100% confident – 67%
80% confident – 60%
Witness confidence is the only statistically significant variable.
Conclusions
The evidence in this field is consistent in showing that confidence is a poor predictor of witness accuracy. Furthermore, the trust that jurors place in the confidence of the witness is undiminished even if the judge advised the jury to be wary of it.
“You can be 100% confident and 100% wrong.”
Penrod and Cutler (1995) Evaluation
– The difference in convictions based upon witness confidence is only slightly above chance.
+ Usefulness – the results of this study can be used by the defence and the prosecution.
+ Construct Validity – supports the view the witness confidence affects convictions – Yale Model of Persuasion.
– Ethnocentrism – the study only used Undergraduates. This is not a representative sample and therefore cannot be generalised to other countries or even the legal system in the USA.
+ Quantitative Data – The quantitive data is easy to compare and analyse, which makes it easy to establish cause and effect through statistical significance.
Audio Podcast
References
Penrod and Cutler, (1995) ‘Witness Confidence and Witness Accuracy: Assessing their Forensic Relation’, Psychology, Public Policy and Law 1 (4), 817–45.
Further Reading
OCR A2 Psychology Student Unit Guide: Unit G543: Forensic Psychology (Student Unit Guides)
