Gary L. Wells

Eyewitness Identification Procedures: Recommendations for Lineups and Photospreads

There is increasing evidence that false eyewitness identification is the primary cause of the conviction of innocent people. In 1996, the American Psychology/Law Society and Division 41 of the American Psychological Association appointed a subcommittee to review scientific evidence and make recommendations regarding the best procedures for constructing and conducting lineups and photospreads. Three important themes from the scientific literature relevant to lineup methods were identified and reviewed, namely relative-judgment processes, the lineups-as-experiments analogy, and confidence malleability. Recommendations are made that double-blind lineup testing should be used, that eyewitnesses should be forewarned that the culprit might not be present, that distractors should be selected based on the eyewitnesss verbal description of the perpetrator, and that confidence should be assessed and recorded at the time of identification. The potential costs and benefits of these recommendations are discussed.

Distraction Can Enhance or Reduce Yielding to Propaganda: Thought Disruption Versus Effort Justification

Two experiments were conducted to test competing accounts of the distractionpersuasion relationship, thought disruption and effort justification, and also to show that the relationship is not limited to counterattitudinal communication. Experiment 1 varied distraction and employed two discrepant messages differing in how easy they were to counterargue. In accord with the thought disruption account, increasing distraction enhanced persuasion for a message that was readily counterarguable, but reduced persuasion for a message that was difficult to counterargue. The effort notion implied no interaction with message counterarguability. Experiment 2 again varied distraction but the two messages took a nondiscrepant position. One message elicited primarily favorable thoughts and the effect of distraction was to reduce the number of favorable thoughts generated; the other, less convincing message elicited primarily counterarguments, and the effect of distraction was to reduce counterarguments. A Message X Distraction interaction indicated that distraction tended to enhance persuasion for the counterarguable message but reduce persuasion for the message that elicited primarily favorable thoughts. The experiments together provided support for a principle having greater generality than the Festinger-Maccoby formulation: Distraction works by inhibiting the dominant cognitive response to persuasive communication and, therefore, it can result in either enhanced or reduced acceptance.

Stimulus Sampling and Social Psychological Experimentation

The authors discuss the problem with failing to sample stimuli in social psychological experimentation. Although commonly construed as an issue for external validity, the authors emphasize how failure to sample stimuli also can threaten construct validity. They note some circumstances where the need for stimulus sampling is less obvious and more obvious, and they discuss some well-known cognitive biases that can contribute to the failure of researchers to see the need for stimulus sampling. Data are presented from undergraduate students (N = 106), graduate students (N = 72), and psychology faculty (N = 48) showing insensitivity to the need for stimulus sampling except when the problem is made rather obvious. Finally, some of the statistical implications of stimulus sampling with particular concern for power, effect size estimates, and data analysis strategies are noted.

Eyewitness Evidence: Improving Its Probative Value

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 eyewitnesss 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 Münsterbergs 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.

Mental Simulation of Causality

We propose that people imagine alternatives to reality (counterfactuals) in assessing the causal role of a prior event. This process of mental simulation (Kahneman & Tversky, 1982) is used to derive novel predictions about the effects of default events on causal attribution. A default event is the alternative event that most readily comes to mind when a factual event is mentally mutated. The factual event is judged to be causal to the extent that its default undoes the outcome. In Experiment 1, a woman was described as having died from an allergic reaction to a meal ordered by her boss. When the boss was described as having considered another meal without the allergic ingredient, people were more likely to mutate his decision and his causal role in the death was judged to be greater than when the alternative meal was also said to have the allergic ingredient. In Experiment 2, a paraplegic couple was described as having died in an auto accident after having been denied a cab ride. People perceived the cabbys refusal to take the couple as a stronger cause of the deaths when his taking the couple would have undone the accident than when it would have not have. We conclude that an adequate theory of causal judgment requires an understanding of these counterfactual simulations.

From the Lab to the Police Station A Successful Application of Eyewitness Research

The U.S. Department of Justice released the first national guide for collecting and preserving eyewitness evidence in October 1999. Scientific psychology played a large role in making a case for these procedural guidelines as well as in setting a scientific foundation for the guidelines, and eyewitness researchers directly participated in writing them. The authors describe how eyewitness researchers shaped understanding of eyewitness evidence issues over a long period of time through research and theory on system variables. Additional pressure for guidelines was applied by psychologists through expert testimony that focused on deficiencies in the procedures used to collect the eyewitness evidence. DNA exoneration cases were particularly important in leading U.S. Attorney General Janet Reno to notice the eyewitness literature in psychology and to order the National Institute of Justice to coordinate the development of national guidelines. The authors describe their experience as members of the working group, which included prosecutors, defense lawyers, and law enforcement officers from across the country.

The confidence-accuracy relationship in eyewitness identification: effects of lineup instructions, foil similarity, and target-absent base rates

Discriminating accurate from mistaken eyewitness identifications is a major issue facing criminal justice systems. This study examined whether eyewitness confidence assists such decisions under a variety of conditions using a confidence-accuracy (CA) calibration approach. Participants (N = 1,200) viewed a simulated crime and attempted 2 separate identifications from 8-person target-present or target-absent lineups. Confidence and accuracy were calibrated for choosers (but not nonchoosers) for both targets under all conditions. Lower overconfidence was associated with higher diagnosticity, lower target-absent base rates, and shorter identification latencies. Although researchers agree that courtroom expressions of confidence are uninformative, our findings indicate that confidence assessments obtained immediately after a positive identification can provide a useful guide for investigators about the likely accuracy of an identification.

The Undoing of Scenarios

Scenarios with dramatic outcomes often evoke counterfactual thinking, mentally undoing that outcome by mutating events in the causal scenario and thereby allowing for the mental simulation of new outcomes. Is Experiment 1, we manipulated the order of four events in a scenario. Each of these events could be mutated to alter the outcome, and each event was described as having caused the eveni that followed it People preferred to change the first event and showed no preference for changes to the subsequent events. We proposed that perceived mutability of an event is constrained by the existence of prior events that are believed to have caused the event. Experiment 2 examined characteristics of the events themselves, rather than their order, that affect their mutability. When these were framed as a norm, people were relatively unlikely to mutate the event in order to undo the outcome, instead preferring to mutate the exceptions. The norm or exception status of other events in the scenario did not affect the mutability of a focal event. Discussion includes the conditions that naturally trigger counterfactual thinking and the role of counterfactual thinking in affective reactions.

Guidelines for Empirically Assessing the Fairness of a Lineup

Issues regarding the fairness of lineups used for criminal identification are discussed in the context of a distinction between nominal size and functional size. Nominal size (the number of persons in the lineup) is less important for determining the fairness of a lineup than is functional size (the number of lineup members resembling the criminal). Functional size decreases to the extent that the nonsuspect members of the lineup are easily ruled out as not being suspected by the police. The extent to which the identification of the suspect can be considered an independently derived piece of incriminating evidence is positively related to functional size. Empirical estimates of functional size can be obtained through pictures of the corporal lineup from which mock witnesses make guesses of whom they believe the police suspect. A distinction is made between a functional size approach and hypothesis testing approaches. Uses of functional size notions in the court, by police, and in research are discussed.

The selection of distractors for eyewitness lineups

Thefts were staged for 252 eyewitnesses using seven different confederate thieves. Photospreads were constructed for each eyewitness to test a proposal regarding strategies for selecting lineup distractors (C. A. E. Luus & G. L. Wells, 1991). Distractors were selected to resemble a suspect or to match the eyewitnesss description of the culprit. A mismatch-description strategy was included for comparison and contrast with the other two strategies. The match-description strategy produced both a low false-identification rate and a high accurate-identification rate. The mismatch-description strategy was unable to hold down false-identification rates, and the resemble-suspect strategy failed to secure acceptable rates of accurate identification