Cutler and Penrod (1989) ‘The Eye Witness, The Expert Psychologist and the Jury.’

Cutler and Penrod (1989) ‘The Eye Witness, The Expert Psychologist and the Jury.’ Law and Human Behaviour


This is the second study we will be looking at from Reaching Verdict and  Persuading a Jury, as part of your OCR A2 Forensic Psychology course. It is further categorised into ‘persuasion’ and ‘expert witnesses.’

Reaching a verdict and Persuading a Jury consider the legal system. This study specifically covers the effects of expert witnesses on jury verdicts.

In the United Kingdom the final verdict in criminal trials is made by a jury of 12 citizens randomly selected from the voting register,  which upon turning 18 all UK citizens are added to. Prisoners and people diagnosed with mental illnesses are not allowed to serve on juries.


Hovland and Janis (1959) – proposed the Yale Model of Persuasion, which suggests that there are a number of factors to consider when attempting to persuade an audience.

They proposed four factors:

  • Source
  • Message
  • Recipients
  • Situation

The Source of the message must appear credible and non-biased.

The message must have some emotional appeal and the most important information should be presented first.

The recipient’s resistance to persuasion is important and this can be reduced by making the situation more informal.

The situation can be made more informal by the use of jokes, eye contact and using the audiences’ first names.


To investigate whether the presence of an expert witness would affect the juror’s decision making ability.

Method and Design

Laboratory experiment using a videotaped mock trial of a robbery.


538 undergraduates who were given extra credits in their introductory Psychology course.


The participants were divided into groups of between 2-8 and were then shown a videotape of a robbery.

There were four independent variables:

  1. Witness Identifying Conditions (Good/Poor)
  2. Witness Confidence (Good/Poor)
  3. Expert Opinion Expressed (High/Low)
  4. Form of Expert Testimony (Descriptive/Statistical)

Witness Identifying Conditions (Good/Poor)

In the good condition the robber did not have a gun, or any disguise. There was a 2 day delay in the witness providing identification.

In the poor condition the robber had a gun and wore a disguise. In this condition there was a 14 day delay in the witness providing identification.

Witness Confidence (Good/Poor)

In the good condition the witness claimed to be 100% confident, whereas, in the poor condition the witness claimed to be only 80% confident of their decision.

Expert Opinion Expressed (High/Low)

In half the trials, the expert witness (The Psychologist) would rate the eyewitness on a scale of 0-25 . Low ratings were given when the participant was in the poor witness identifying conditions group and high ratings to the good witness identifying conditions group.

Form of Expert Testimony (Descriptive/Statistical)

In the descriptive condition, the expert psychologist used ordinary language to describe how different factors can have an impact on the accuracy of eyewitness testimony, whereas, in the statistical condition, the psychologist stated statistics and used a more psychological lexicon, which was likely to baffle the jury. (Evaluative point: the jury in this experiment were Psychology students, so they might not have been baffled by the use of such language. However, these were students on an introductory course to psychology.)

Then the participants completed a questionnaire alone. This questionnaire contained the dependant variables:

  • Dependent Variable 1: Guilty or not guilty?
  • Dependent Variable 2: How confident are your in your verdict?
  • Dependent Variable 3: Memory of the trial and the expert Psychologists testimony.

Jurors gave more guilty verdicts when Witness Identification Conditions were good. This increased if the Psychologist used the simple descriptive language.

Juror confidence was more in the good Witness Identification Conditions. Jurors also expressed more confidence when the eyewitness claimed to be 100% confidence in their identification of the robber.

85% of jurors remembered the trial accurately and memory of the Psychologists testimony was also good. They recalled correctly what the expert had said about weapons focus, disguises and delays in identification.


The expert testimony improved the juror’s knowledge of factors that might affect the accuracy of eyewitness testimony and made them pay more attention to the Witness Identification condition.

There was no evidence to suggest that jurors were skeptical about the eye witness based on the expert Psychologists testimony.

Cutler and Penrod (1989) Evaluation

– Ecological validity is one of the biggest issues for this study. The jury was composed entirely of Psychology students, who are not representative of a jury in real life, which would have a wider range of people and ages. Furthermore, the participants were divided into groups of between 2-8. This is not representative of a jury of 12. In furtherance, the jury saw the crimes on video, which would not happen in a regular trial. However, it could be argued that there was some ecological validity as the jury deliberated in groups, which does not happen in all studies of this kind.

+ Construct Validity – the results show support for the Yale Model of Persuasion.

– Qualitative Data – the lack of qualitative data in this study does not provide us with any detail with which we can further understand that juror’s verdicts.

+ Reliability – both the large sample and the methodology makes this experiment highly reliable.

– Demand Characteristics – As the participants were given course credit for their participation, we can argue that some of the results may be due to participants trying to act in a way desirable to the experimenters.

– Ethnocentrism – the study only used American Psychology students. 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 compere and analyse, which makes it easy to establish cause and effect through statistical significance.

Audio Podcast



Cutler and Penrod (1989) ‘The Eye Witness, The Expert Psychologist and the Jury.’ Law and Human Behaviour


Further Reading

OCR A2 Psychology Student Unit Guide: Unit G543: Forensic Psychology (Student Unit Guides)


Article Name
Cutler and Penrod (1989) 'The Eye Witness, The Expert Psychologist and the Jury.'
Cutler and Penrod (1989) is the second study we will be looking at from Reaching Verdict and Persuading a Jury, as part of your OCR A2 Forensic Psychology course. It is further categorised into 'persuasion' and 'expert witnesses.'