The impact of general versus specific expert testimonyand eyewitness confidence upon mock juror judgment

Subjects (n=128) initially viewed an eyewitness of high or low confidence. Subsequently, participants viewed a psychologist who gave either espert testimony on the unreliability of eyewitness identification, specific expert testimony, or no expert (control) testimony. Subjects viewing expert testimony believed the eyewitness identified the gunman significantly less often, gave the defendant lower guilt ratings, estimated a lower general percentage of correct identifications under similar circumstances, estimated a lower percentage of general accurate eyewitness testimony, and gave significantly lower ratings to the belief that one can generally tell from eyewitness confidence whether an eyewitness is accurate than subjects in control conditions. Significant differences were also obtained between general and specific expert testimony. Participants viewing specific expert testimony estimated lower general percentages of correct identifications under the circumstances of the crime and reported relying more upon the psychologist's testimony than subjects viewing general expert testimony. Additionally, subjects viewing general expert testimony had significantly less confidence in their gunman vs. innocent person decision than subjects in specific testimony or control conditions. Subjects who viewed the high confidence eyewitness decided that the eyewitness correctly identified the gunman more often, gave the defendant higher guilt ratings, and estimated the general percentage of accurate eyewitness testimony to be significantly higher than jurors in low eyewitness confidence groups. The finding that jurors may continue to rely on eyewitness confidence to gauge the accuracy of the witness even after viewing expert testimony is discussed.     

Influence of expert testimony regarding eyewitness accuracy on jury decisions

To determine the influence of expert testimony regarding the general unreliability of eyewitnesses, a two-phase study was conducted. In the first phase, 24 community residents served as jurors on four six-person juries. A burglary case was tried in 120 District Court. El Paso, Texas. Two juries heard all the evidence including the expert testimony of a psychologist and the other two heard all of the testimony except that of the psychologist. During the second phase, 24 student jurors constituting four six-person juries viewed a videotape of the trial. Two of these juries saw the entire proceeding from the first phase including the expert testimony and the remaining two saw all but the expert testimony. All juries acquitted the defendant; however, those who heard the expert testimony significantly lowered their judgments of the accuracy and reliability of eyewitness identification as well as its overall importance to the trial. Further, those juries that heard the expert testimony spent a significantly longer time discussing eyewitness identification as well as other relevant evidence. No differences between community residents and college student juries were obtained.The authors wish to thank Judge Brunson Moore, Mr. David Jeans, Mr. Ricky Glenn Smith, Detective James Christianson, D. Steven Cooper, Rachel Hanna, Daniel Torres, and Patricia Tetreault. All of these people participated in the trial and without them this research could not have been conducted. This research was supported by Gift Funds of the Department of Psychology, University of Texas at El Paso.     

Effects of Experiencing the Eyewitness Identification Procedure on Juror Decisions

Mistaken eyewitness identifications are believed to contribute to a preponderance of wrongful convictions, underscoring the need to identify methods to help decrease the likelihood of false convictions based on eyewitness testimony. The present study tested the hypothesis that providing jurors with first-hand experience with eyewitness identification procedures could help further sensitize them to the limitations of eyewitness testimony. Eighty college students watched a videotaped mock trial in which the prosecution’s sole evidence was eyewitness testimony. In a 2 × 2 randomized factorial design, we manipulated whether participants heard expert psychological testimony (henceforth referred to as expert testimony) on the limitations of eyewitness identification and whether they experienced an eyewitness identification procedure. As predicted, experiencing the eyewitness identification procedure had a significant impact on juror decisions, suggesting that this procedure could further help reduce the likelihood of wrongful convictions.     

Impact of Defense-Only and Opposing Eyewitness Experts on Juror Judgments

Previous research shows that expert testimony on eyewitness memory influences mock-juror judgments. We examined the extent to which opposing expert testimony mitigates the impact of defense-only expert testimony. Participants (N = 497) viewed a video-taped trial involving an eyewitness identification and individually rendered verdicts and evaluated the evidence and the experts. We manipulated the Foils (unbiased vs. biased) and Instructions (unbiased vs. biased) of the lineup and Expert Testimony (no expert vs. defense-only expert vs. opposing experts). Expert testimony did not significantly influence juror judgments, but the opposing expert testimony diminished the credibility of the defense expert in the eyes of the jurors. Results point to the need for further research on conditions that qualify the impact of expert testimony.     

Can experts help jurors to evaluate eyewitness evidence? A review of eyewitness expert effects

Courts occasionally permit psychologists to present expert evidence in an attempt to help jurors evaluate eyewitness identification evidence. This paper reviews research assessing the impact of this expert evidence, which we argue should aim to increase jurors' ability to discriminate accurate from inaccurate identifications. With this in mind we identify three different research designs, two indirectly measuring the expert's impact on juror discrimination accuracy and one which directly assesses its effect on this measure. Across a total of 24 experiments, three have used the superior direct methodology, only one of which provides evidence that expert testimony can improve jurors' ability to discriminate between accurate and inaccurate eyewitness identifications.     

Comparing the effectiveness of <Emphasis Type="Italic">Henderson</Emphasis> instructions and expert testimony: Which safeguard improves jurors’ evaluations of eyewitness evidence?

Objectives

The New Jersey Supreme Court recently determined that jurors may not be able to effectively evaluate eyewitness evidence on their own. As a result, the Court proposed the use of judicial instructions to assist jurors (called Henderson instructions) and suggested the implementation of these instructions would reduce the need for expert testimony. We tested the efficacy of these instructions compared to alternative instructions and expert testimony.

Methods

We utilized a mock trial paradigm, randomly assigning 452 participants to 1 of 20 videotaped trial conditions that varied the quality of eyewitness evidence (both witnessing and identification conditions) and the type of safeguard presented during the mock trial.

Results

Jurors were sensitive to the quality of identification conditions on their own. Jurors were more likely to convict when identification conditions were good and less likely when identification conditions were poor. This relationship was mediated by eyewitness credibility ratings. Expert testimony resulted in skepticism by reducing the likelihood that jurors would convict regardless of the quality of witnessing and identification conditions. No variation of the instructions influenced verdicts.

Conclusions

While jurors were sensitive to the quality of identification conditions on their own, we observed no such effect for the quality of witnessing conditions, even with the aid of instructions and/or expert testimony. Both Henderson instructions and expert testimony may be insufficient for assisting jurors to effectively evaluate problematic witnessing conditions. Future research should examine the use of alternative safeguards.

     

Expert psychological testimony

Experimental psychologists increasingly are asked to give expert testimony in court, especially with regard to issues of eyewitness reliability. Whether or not experimental psychologists should give expert testimony on these matters is a controversial issue. The empirical literature suggests that potential jurors do not have a good understanding of the variables influencing eyewitness accuracy and that they cannot discriminate adequately between accurate and false eyewitness identification testimony. Experiments using expert testimony as a treatment variable, however, have not made a definitive case that expert testimony can benefit trial outcomes. The question of whether or not to give expert testimony must be broadened to consider not only the effects on verdicts but also the effects of expert testimony on the process by which verdicts are reached, the practices of police in subsequent investigations, the public's view of psychology, the practices of judges in subsequent cases, and the interaction between expert testimony and research activities.     

A comparison of three studies of the influence of expert testimony on jurors

Three conceptual replications of the effects of expert testimony on jurors' decisions and behaviors were compared. Taken together, these studies demonstrated significant increases in jurors' scrutiny of the evidence presented to them and significant reductions in their beliefs in the general accuracy of eyewitness testimony. The overall effect of expert testimony had a combined probability ofp=.0000084. This means that these combined results would occur by sampling bias alone less than one time out of 100,000. Expert testimony accounted for 3% of the variance in verdicts and 68% of the variance in the time jurors deliberated about eyewitness testimony. Several implications of these findings for psychologists investigating eyewitness identification and for the criminal justice system are discussed.I would like to thank James V. Devine, Judith P. Goggin, Elizabeth F. Loftus, and Gary L. Wells for their valuable comments on an earlier draft of this article.     

Two conjectures about the issue of expert testimony

This article responds to concerns about expert testimony in experimental psychology by conjectur that disagreements about the propriety of the testimony are camouflaged arguments about the strength of psychological knowledge. Differences between proponents and opponents of expert testimony are about the state of psychological knowledge and certainty, rather than about the proper standard for psychologists to use when deciding whether to testify. A second conjecture is stimulated by the assumption that laypersons generally overvalue eyewitness testimony and that expert psychological testimony is a required corrective. The truth of this assumption rests on the debatable assertions that eyewitness identifications, without more, are potent sole determinants of trial outcome, and that lay juries need instruction from experimental psychologists about aspects of human behavior of which the jurors are definitive producers and consumers. One need not resolve these debates in order to understand that psychologists should not rely on the legal community to set the psychologists' standards for expert testimony. And psychologists, in considering their role as courtroom experts, should guard against a self-serving critique of the acumen of lay juries.     

Psychological factors in eyewitness identifications

It has been suggested that incorrect eyewitness identifications have led to more miscarriages of justice than all other factors combined. Several issues which are likely to affect the accuracy of eyewitness identifications are discussed. Research on the impact of race on identifications has illustrated an “own-race bias” in identification accuracy, but it is not yet clear to what extent this bias is related to racial prejudice or amount of cross-racial experience. Although the U.S. Supreme Court has suggested that eyewitnesses who are more certain of their identifications are more likely to be correct, research on this issue has yielded mixed results. Because of its fallible nature, some writers have argued that eyewitness evidence should be used sparingly or not at all in the judicial process. Other suggestions highlight procedures for minimizing bias and providing legal safeguards for the suspect during the identification process, or educating jurors about the potential fallibility of eyewitness evidence by means of judge's cautionary jury instructions or by the use of researchers as expert witnesses. Controversial issues concerning researchers as expert witnesses are discussed.     

Error Rates,Likelihood Ratios,and Jury Evaluation of Forensic Evidence

Forensic examiners regularly testify in criminal cases, informing the jurors whether crime scene evidence likely came from a source. In this study, we examine the impact of providing jurors with testimony further qualified by error rates and likelihood ratios, for expert testimony concerning two forensic disciplines: commonly used fingerprint comparison evidence and a novel technique involving voice comparison. Our method involved surveying mock jurors in Amazon Mechanical Turk (N = 897 laypeople) using written testimony and judicial instructions. Participants were more skeptical of voice analysis and generated fewer “guilty” decisions than for fingerprint analysis (B = 2.00, OR = 7.06, p = <0.000). We found that error rate information most strongly decreased “guilty” votes relative to no qualifying information for participants who heard fingerprint evidence (but not those that heard voice analysis evidence; B = −1.16, OR = 0.32, p = 0.007). We also found that error rates and conclusion types led to a greater decrease on “guilty” votes for fingerprint evidence than voice evidence (B = 1.44, OR = 4.23, p = 0.021). We conclude that these results suggest jurors adjust the weight placed on forensic evidence depending on their prior views about its reliability. Future research should develop testimony and judicial instructions that can better inform jurors of the strengths and limitations of forensic evidence.     

Courtroom testimony by psychologists on eyewitness identification issues

This article makes two major points in regard to expert psychological testimony on eyewitness identification. First, the attention devoted by psychologists to eyewitness identification issues is far out of proportion to the incidence of trials involving eyewitness identifications of criminal defendants; furthermore, the often-expressed concern over wrongful convictions is probably misplaced. Second, the experimental methods used in studies of eyewitness performance are fundamentally unsuited for drawing conclusions about actual witnesses. Hence, there is not an adequate scientific foundation for expert psychological testimony on eyewitness identification. Archival research is perhaps the most promising approach to the study of the criminal justice system.     

Complex scientific testimony: How do jurors make decisions?

Critics of the civil jury system question whether jurors can adequately evaluate complex expert testimony. Based on current models of research in persuasion, we hypothesized that when expert testimony is complex, factors other than content will influence persuasion. Participants, serving as mock jurors, watched a videotaped trial in which two scientists provided evidence on whether PCBs could have caused a plaintiff's illness. The complexity of the expert's testimony and the strength of the expert's credentials were varied in a 2×2 factorial design. After watching the videotape, mock jurors rendered a verdict and completed a number of attitude measures related to the trial. Overall, consistent with our prediction, we found that jurors were more persuaded by a highly expert witness than by a less expert witness, but only when the testimony was highly complex. When the testimony was less complex, jurors relied primarily on the content of that testimony, and witness credentials had little impact on the persuasiveness of the message.     

Considering forensic science: individual differences,opposing expert testimony and juror decision making

Two experimental studies examined the effect of opposing expert testimony on perceptions of the reliability of unvalidated forensic evidence (anthropometric facial comparison). In the first study argument skill and epistemological sophistication were included as measures of individual differences, whereas study two included scores on the Forensic Evidence Evaluation Bias Scale. In both studies participants were assigned to groups who heard: (1) no expert testimony, (2) prosecution expert testimony, or (3) prosecution and opposing expert testimony. Opposing expert testimony affected verdict choice, but this effect was mediated by perceptions of reliability of the initial forensic expert's method. There was no evidence for an effect on verdict or reliability ratings by argument skill or epistemology. In the second experiment, the same mediation effect was found, however scores on one subscale from the FEEBS and age also affected both verdict and methodological reliability. It was concluded that opposing expert testimony may inform jurors, but perceptions of the reliability of forensic evidence affect verdict, and age and bias towards forensic science influence perceptions of forensic evidence. Future research should investigate individual differences that may affect perception or bias towards forensic sciences under varying conditions of scientific reliability.     

Jurors'Evaluations of Expert Testimony: Judging the Messenger and the Message

Jurors are laypersons with no specific expert knowledge, yet they are routinely placed in situations in which they need to critically evaluate complex expert testimony. This paper examines jurors'reactions to experts who testify in civil trials and the factors jurors identify as important to expert credibility. Based on in-depth qualitative analyses of interviews with 55 jurors in 7 civil trials, we develop a comprehensive model of the key factors jurors incorporate into the process of evaluating expert witnesses and their testimony. Contrary to the frequent criticism that jurors primarily evaluate expert evidence in terms of its subjective characteristics, the results of our study indicate that jurors consider both the messenger and the message in the course of evaluating the expert's credibility.     

Ten years in the life of an expert witness

American Courts are experiencing increased use of expert testimony based upon psychological research. Ten years ago, I began testifying about my own research on human perception, recollection, and eyewitness accounts. The growing acceptance of this testimony percipitated a backlash from some psychologists. This essay describes the chronology of these events, and their relevance for the more general use of psychological research as evidence in court.     

The Impact of Eyewitness Expert Evidence and Judicial Instruction on Juror Ability to Evaluate Eyewitness Testimony

It has been argued that psychologists should provide expert evidence to help jurors discriminate between accurate and inaccurate eyewitness identifications. In this article we compare the effects of judicial instruction with expert evidence that is either congruent or incongruent with the ground truth, focusing on juror ability to evaluate “real” eyewitness evidence. In contrast to studies which have employed “fictional” eyewitness designs, we found no appreciable effect of either congruent or incongruent expert evidence on participant-juror sensitivity to eyewitness accuracy. We discuss the role of methodology on the inferences and conclusions that can be made regarding the impact of eyewitness expert evidence.