Eyewitness Evidence Improving Its Probative Value

Psychological Science in the Public Interest 11/2006; 7(2). DOI: 10.1111/j.1529-1006.2006.00027.x


The criminal justice system relies heavily on eyewitnesses to determine the facts surrounding criminal events. Eyewitnesses may identify culprits, recall conversations, or remember other details. An eyewitness who has no motive to lie is a powerful form of evidence for jurors, especially if the eyewitness appears to be highly confident about his or her recollection. In the absence of definitive proof to the contrary, the eyewitness's account is generally accepted by police, prosecutors, judges, and juries. However, the faith the legal system places in eyewitnesses has been shaken recently by the advent of forensic DNA testing. Given the right set of circumstances, forensic DNA testing can prove that a person who was convicted of a crime is, in fact, innocent. Analyses of DNA exoneration cases since 1992 reveal that mistaken eyewitness identification was involved in the vast majority of these convictions, accounting for more convictions of innocent people than all other factors combined. We review the latest figures on these DNA exonerations and explain why these cases can only be a small fraction of the mistaken identifications that are occurring. Decades before the advent of forensic DNA testing, psychologists were questioning the validity of eyewitness reports. Hugo Münsterberg's writings in the early part of the 20th century made a strong case for the involvement of psychological science in helping the legal system understand the vagaries of eyewitness testimony. But it was not until the mid- to late 1970s that psychologists began to conduct programmatic experiments aimed at understanding the extent of error and the variables that govern error when eyewitnesses give accounts of crimes they have witnessed. Many of the experiments conducted in the late 1970s and throughout the 1980s resulted in articles by psychologists that contained strong warnings to the legal system that eyewitness evidence was being overvalued by the justice system in the sense that its impact on triers of fact (e.g., juries) exceeded its probative (legal-proof) value. Another message of the research was that the validity of eyewitness reports depends a great deal on the procedures that are used to obtain those reports and that the legal system was not using the best procedures. Although defense attorneys seized on this nascent research as a tool for the defense, it was largely ignored or ridiculed by prosecutors, judges, and police until the mid 1990s, when forensic DNA testing began to uncover cases of convictions of innocent persons on the basis of mistaken eyewitness accounts. Recently, a number of jurisdictions in the United States have implemented procedural reforms based on psychological research, but psychological science has yet to have its fullest possible influence on how the justice system collects and interprets eyewitness evidence. The psychological processes leading to eyewitness error represent a confluence of memory and social-influence variables that interact in complex ways. These processes lend themselves to study using experimental methods. Psychological science is in a strong position to help the criminal justice system understand eyewitness accounts of criminal events and improve their accuracy. A subset of the variables that affect eyewitness accuracy fall into what researchers call system variables, which are variables that the criminal justice system has control over, such as how eyewitnesses are instructed before they view a lineup and methods of interviewing eyewitnesses. We review a number of system variables and describe how psychological scientists have translated them into procedures that can improve the probative value of eyewitness accounts. We also review estimator variables, variables that affect eyewitness accuracy but over which the system has no control, such as cross-race versus within-race identifications. We describe some concerns regarding external validity and generalization that naturally arise when moving from the laboratory to the real world. These include issues of base rates, multicollinearity, selection effects, subject populations, and psychological realism. For each of these concerns, we briefly note ways in which both theory and field data help make the case for generalization.
© 2006 Association for Psychological Science.

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Available from: Gary L. Wells, Oct 20, 2014
    • "Composites with even higher naming (M = 45%) were produced when just internal features were shown, with external features added thereafter (Frowd et al., 2012d); for an example face array, see Fodarella et al. (2015b). A further important development was made by facilitating holistic processing prior to face construction (Frowd et al., 2012a): after witnesses have freely recalled a target using CI techniques (e.g., Wells et al., 2007), they reflect silently on its character for one minute and then make seven whole-face judgements—such as its level of perceived honesty or masculinity. These two whole-face techniques, when used after a face-recall CI, form the holistic-cognitive interview (H-CI). "
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    • "We note two important limitations in the use of confidence to assess accuracy. First, the confidence–accuracy relationship is not as strong for negative responses (i.e., identifying no one) as it is for positive responses (i.e., identifying someone; Brewer & Wells, 2006; Sporer et al., 1995). The implication of the differing relationships for positive and negative responses is that lawyers, judges, and juries may be able to reliably distinguish between correct and false identifications based on witness confidence but may be much less able to distinguish between correct and false non-identifications based on witness confidence. "
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    • "By their nature the influence of estimator can never be truly known. While great progress has been made in quantifying and controlling system variables (e.g.,Wells et al., 1998;Wells, Malpass, Lindsay, Fisher, Turtle & Fulero, 2000;Wells, Memon, & Penrod, 2006) the problem of quantifying estimator variable persists. However, the recent proliferation of closed-circuit television (CCTV) cameras (suggested to be between 4 million and 5.9 million in the UK, Security NewsDesk, 2015), offers a potential solution to the estimation problem. "

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