Realism of confidence in witness identification of faces and voices

University dissertation from Uppsala : Acta Universitatis Upsaliensis

Abstract: One of the more alarming and intriguing results in forensic psychology is the weakrelationship between confidence and accuracy in experimental studies of eyewitnessidentification. This relationship has traditionally been measured by the point-biserialcorrelation coefficient, rpb. In the present thesis the confidence-accuracy relationship inwitness identification is studied with two alternative indices, namely calibration anddiagnosticity analysis. When calibration analysis is applied to eyewitness identification,the participant (witness) is required to assess on a scale the subjective probability thatthe identified person is identical to the culprit. The subjective probabilities are comparedto the corresponding relative frequencies of correct identifications. With the use ofdiagnosticity analysis of confidence, which is based on a modified form of Bayes'theorem, it is possible to determine the informational impact of positive identificationsmade with different levels of confidence.In Study I, a number of flaws in earlier studies of the confidence-accuracyrelationship were discussed and theoretical and empirical arguments for the use ofcalibration and diagnosticity analysis were made. It was concluded that eyewitnessconfidence can be both well calibrated and diagnostic, despite a low rpb Study II showed that in comparison to eyewitness identification in similar circumstances, earwitness accuracy is poorer, with overconfidence and low diagnosticity of confidence, even in easy tasks. In Study III, a meta-analysis showed that the measures rpb and calibration were weakly correlated. A modest relation was observed between the rpb and thediagnosticity index. The calibration and over/undercontidence scores co-varied withtask difficulty. As in Study II, overconfidence was observed for voice identificationtasks. In Study IV, self-reported holistic encoding strategy and a high self-reportedability to remember faces were predictive of identification accuracy and associated witha higher confidence-accuracy relation. In contrast, degree of self-reported generalmemory skill was not diagnostic of identification performance. It is suggested that future investigation of the confidence-accuracy relationship in witness identification can benefit from a supplementary use of the alternative measures. Finally, reconstructivememory processes and the malleability of confidence as threats to the usefulness ofconfidence in real legal trials are discussed.

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