A Methodical Review of “Effects of the Type of Incident and the Number of Perpetrators on Eyewitness Memory” by Clifford and Hollin (1981)
The study examines the problem of eyewitness memory in two situations. First, when one witnesses non-violent event (asking directions), and second, when event in question is of a violent character (mugging). The researchers were interested to what extent the number of perpetrators influences the accuracy of identification. Another issue that the authors investigated was the relation of the accuracy of investigation to eyewitness’ subjective feeling of confidence.
The study answered the following research questions:
Do the accuracy of identification differ in the case of violent and non-violent incidents?
How the reliability of eyewitnesses is affected by the number of perpetrators?
What is the relationship between the accuracy of identification and the eyewitness’ confidence in his testimony?
The research design was experimental. Six black-and-white videotapes were used in the experiment. Three of them depicted a violent incident, the rest – a non-violent incident. In the video with one perpetrator, the thief was shown both in profile and in a full-face view. He mugged a bag from woman’s hands and ran away. In the situation, where three perpetrators participated, the thief acted in the same way and was accompanied by two other men who stood close to the victim. The same action was taped in the five-men condition. In the videos that depicted the non-violent condition, the male actor asked the woman direction. The visibility of the actors was the same. As in the case of the violent incident, the action for non-violent condition was repeated with 3 and 5 actors. The same actors participated in both violent and non-violent incident and their movements were uniform for both conditions. An average length of videotapes for violent and non-violent conditions was 12.2 seconds and 12.1 respectively.
Sixty subjects: equal number of males and females, participated in the study on the voluntary basis. All the participants were undergraduate students of North East London Polytechnic. Their age ranged from 17 to 41 years with mean of 21.7 years. Subjects were randomly assigned to the viewing, without any instructions, of one of the six videotapes. After screening, the subjects filled in detailed questionnaires with age, height, weight, sex, race and clothing of the perpetrator. Further, they tried to identify the leading actor from a display of 10 face photographs. Sometimes, the order of these actions was reversed. Confidence in the accuracy was rated from 1 – not at all confident to 7 – very confident.
Independent variables: the number of perpetrators, violent vs. non-violent condition, confidence; dependent variable: accuracy of testimony and of identification.
General findings
The study found that violent character of event significantly decreased the accuracy of testimony. Besides, the accuracy of testimony was negatively correlated with the number of perpetrators, especially in the case of violent event. What is important, under the violent conditions, there was no positive correlation between the accuracy of identification and subject’s confidence, even though it is a commonly held belief that violent crimes increase the accuracy of the eyewitness memory. Overall, the accuracy of identification was low; about one quarter of the subjects (27%) correctly identified a perpetrator. The number of correct identification did not significantly differ in the violent and non-violent incidents.
The conclusions that can be made as a result of this study is that, generally speaking, human memory is not very reliable. This is why, the criminal justice system should cautiously examine the eyewitness testimony, especially when the observed event is of a violent character.
In this study, no deception was used. There is no information about the protection of the subjects. If I were the researcher of this study, I would have also studied the effect of the race of the perpetrator on the accuracy of the eyewitness memory. Overall, I do not see any ethical problem in the research design and its implementation.
Reference:
Clifford, B. R. and Hollin, C. R. (1981). Effects of the Type of Incident and the Number of Perpetrators on Eyewitness Memory. Journal of Applied Psychology, 66(3), (1981): 364-370.
