Educating Jurors about Forensic Evidence: Using an Expert Witness and Judicial Instructions to Mitigate the Impact of Invalid Forensic Science Testimony

Invalid expert witness testimony that overstated the precision and accuracy of forensic science procedures has been highlighted as a common factor in many wrongful conviction cases. This study assessed the ability of an opposing expert witness and judicial instructions to mitigate the impact of invalid forensic science testimony. Participants (N = 155) acted as mock jurors in a sexual assault trial that contained both invalid forensic testimony regarding hair comparison evidence, and countering testimony from either a defense expert witness or judicial instructions. Results showed that the defense expert witness was successful in educating jurors regarding limitations in the initial expert's conclusions, leading to a greater number of not-guilty verdicts. The judicial instructions were shown to have no impact on verdict decisions. These findings suggest that providing opposing expert witnesses may be an effective safeguard against invalid forensic testimony in criminal trials.     

The importance of forensic evidence for decisions on criminal guilt

Recent studies have found that the general public perceives forensic evidence to be relatively inaccurate and to involve high levels of human judgement. This study examines how important the general public finds forensic evidence by comparing decisions on guilt and punishment in criminal cases that involve forensic versus eyewitness testimony evidence and examining whether a CSI effect exists. Specifically, this experimental survey study utilized a 2 (crime type: murder or rape) × 4 (evidence type: DNA, fingerprint, victim eyewitness testimony, or bystander eyewitness testimony) ? 1 (no victim testimony for murder scenario) design, yielding seven vignettes scenarios to which participants were randomly assigned. Results indicate that forensic evidence was associated with more guilty verdicts and higher confidence in a guilty verdict. Forensic evidence did not change the expected sentence length and did not generally affect the ideal sentence length. However, for rape, respondents believed that the defendant should receive a longer sentence when forensic evidence was presented but forensic evidence did not alter likely sentence that respondents expected the defendant to receive. The results of this study did not support a CSI effect. Overall, this study suggests that forensic evidence – particularly DNA – has a stronger influence during the verdict stage than the sentencing stage.     

Expert Testimony Regarding Child Witnesses: Does It Sensitize Jurors to Forensic Interview Quality?

Does expert testimony on forensic interviews with children help adults distinguish between poorly conducted and well-conducted interviews? This study evaluates the effects of social framework expert testimony regarding child witnesses in a case involving allegations of child sexual abuse. A 2 (Expert Testimony: present or absent) × 3 (Child Forensic Interview Quality: poor, typical, or good) × 2 (Child’s Age: 4- or 10-year-old) factorial design was used to examine whether expert testimony is prejudicial or beneficial to jurors (N = 463). The results revealed that, without expert testimony, mock jurors did not consider the forensic interview quality when reaching a verdict. However, with expert testimony, mock jurors were more likely to render guilty verdicts if the interview quality was good versus poor. Further expert testimony increased mock jurors’ knowledge about child witnesses. These findings suggest that expert testimony related to the impact of interview techniques on the reliability of children’s reports may assist fact-finders in evaluating child abuse cases.     

The Impact of Negative Forensic Evidence on Mock Jurors’ Perceptions of a Trial of Drug-Facilitated Sexual Assault

Legal concerns with regard to the adverse impact of a negative toxicological screening for date-rape drugs in a case of drug-facilitated sexual assault (DFSA) were the focus of a recent Canadian case (R. v. Alouache, 2003). To assess the impact of a negative forensic report, as well as the impact of expert testimony explaining the many factors that may contribute to a negative outcome, participants (N=171) received a written trial stimulus in which the forensic evidence (negative report, negative report plus expert testimony, no negative report and no expert testimony control) and the complainant's beverage consumption (alcohol, cola) were systematically varied. Results indicate that a negative finding in the absence of expert testimony produced greater verdict leniency and more favourable evaluations of the defendant's case. In contrast, no differences were found between the case in which the expert testified and a case in which the negative report and expert testimony were omitted.

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The Testimony of Forensic Identification Science: What Expert Witnesses Say and What Factfinders Hear

This research examined how variations in the presentation of forensic science information affect factfinders’ judgments in a trial. Participants read a summary of a murder case, the critical testimony being the results of a microscopic hair comparison given by a forensic expert. Across two experiments we manipulated how the expert expressed his results, whether he gave an explicit conclusion concerning identity of the hair, and whether the limitations of forensic science were expressed during trial. Qualitative testimony was more damaging to the defense than quantitative testimony, conclusion testimony increased the defendant’s culpability ratings when findings were presented quantitatively, and expressing limitations of forensic science had no appreciable effect. Results are discussed in terms of factfinders’ interpretation of forensic identification evidence.     

Barring ultimate issue testimony

This research focuses on one of the major changes wrought by the Insanity Defense Reform Act of 1984: the exclusion of expert mental health testimony on the “ultimate issue,” that is, testimony specifically addressing the expert's opinion that the defendant is sane or insane. Subjects in this research were presented with 1 of 10 variants of an insanity case in which experts testified for the defense, prosecution, both, or neither. The testimony was at one of three levels: diagnostic only, penultimate issue, or ultimate issue. Results showed that level of testimony had no effect on the verdict pattern. There was evidence to suggest that this effect may occur because jurors infer, and/or mistakenly recall, higher levels of expert testimony than was actually presented to them. In addition, general and specific constructs (Finkel & Handel, 1989) that predict verdict yieldedR ² values from .500 to .668 and were not significantly affected by the level of expert testimony. Implications of these findings are discussed.     

科学证据可采性规则研究

科学证据是运用科学知识和科学方法对证据分析所得的判断意见。因此,科学证据属于意见性证言。为防止不可靠的科学证据对法庭的误导,英美法系国家建立了科学证据可采性规则,包括相关性规则、必要性规则、专家证人资格规则、排除规则、可靠性规则。美国科学证据可靠性规则经历了从Frye规则、Daubert规则到修订后的《联邦证据规则》702条的嬗变。我国对鉴定意见的审查主要限于相关性和合法性的审查。由于缺少对鉴定意见可靠性审查的指导与限制,导致了错误裁决的风险。本文提出确立鉴定意见科学可靠性规则的构想,以利于法官排除错误的鉴定意见,同时有助于法庭科学实验室的管理与制度完善,促使法庭科学实验室更严谨更科学地为法庭提供优质的法庭科学服务。     

中国刑事专家辅助人向专家证人的角色转变

中国的刑事专家辅助人具有既类似于律师又类似于鉴定人、证人的多重属性;围绕专家辅助人意见的性质,也形成了质证方式说、鉴定意见说、证人证言说等多种观点。角色定位上的混乱,不仅造成了独具特色的鉴定人与专家辅助人的双轨制,而且常常使专家辅助人意见的法庭采信陷入困境。从最高人民法院有关专家辅助人的新近规定看,专家辅助人的角色呈现出向专家证人转变的趋势。这种转变的核心要求,一是实现鉴定人和专家辅助人的诉讼地位平等,专家辅助人意见和鉴定意见在专家证言意义上的证据效力平等;二是使专家辅助人回归专家证人本色,将强加给专家辅助人的不合理的质证职责交还给律师、检察官;三是提高律师、检察官熟练运用交叉询问规则、对科学证据进行质证的能力,充分发挥法官的科学证据“守门人”作用,以适应事实认定科学化的需要。     

Does Ambivalent Sexism Influence Verdicts for Heterosexual and Homosexual Defendants in a Self-Defense Case?

The current research examined the role of defendant and participant sex, presence or absence of expert testimony of the “battered person syndrome”, and sexual orientation of the defendant on perceptions of guilt in a self-defense case. The role of sexism in judgments of culpability was also examined. A sample of 442 participants read a self-defense case scenario and responded to questions pertaining to verdict, defendant culpability, legal element ratings, and sexist attitudes. Results revealed a four-way interaction, showing female participants prescribed the lowest guilt ratings to heterosexual female and homosexual male defendants who received expert testimony of the battered person syndrome. When heterosexual male defendants received expert testimony, ratings of guilt significantly increased. A multiple regression was conducted to determine whether legal and extra-legal factors predicted defendant culpability. Sexist attitudes (benevolent sexism towards men and women) and certain legal elements were predictive of defendant culpability. Limitations and implications are discussed. Study findings were presented in a poster at the annual meeting of the American Psychology-Law Society (APLS), Jacksonville, Florida (March, 2008).     

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.     

The power of presentation: How attire,cosmetics, and posture impact the source credibility of women expert witnesses

Gender stereotypes may negatively affect perceptions of women professionals' credibility, including forensic experts. This study investigated the impact of behavior-based and appearance-based factors on women expert witness's credibility. Jury-eligible adults were shown one of 16 conditions depicting a woman expert which varied based on combinations of three primary independent variables: (1) attire, (2) cosmetic use, and (3) posture. Expert attractiveness and participants' sexist attitudes served as covariates. Results revealed that women experts were seen as marginally more credible when wearing a skirt suit with a closed posture stance than when wearing a pant suit with a closed posture. Secondary analyses indicated expert attractiveness and participant sexist attitudes accounted for the most variability in credibility scores. Credibility of women expert witnesses may be impacted by irrelevant peripheral cues. Findings can inform discussions aimed at mitigating extraneous factors that inadvertently undermine the reception of women expert witness testimony.     

Identifying and measuring juror pre-trial bias for forensic evidence: development and validation of the Forensic Evidence Evaluation Bias Scale

Abstract

Previous research has provided support for the impact of juror pre-trial bias on judicial decision making, particularly in cases where the evidence presented at trial is of weak or ambiguous probative value. In an effort to identify whether a pre-trial bias for forensic evidence exists, the Forensic Evidence Evaluation Bias Scale (FEEBS) was developed and tested. The results of a principal components analysis suggested that two distinct constructs were being measured, corresponding to a pro-prosecution and pro-defence bias toward forensic evidence. In a second validation study, scores on these two subscales were compared with other existing juror bias measures (Juror Bias Scale and Belief in a Just World) and in a mock juror decision making task only the pro-prosecution subscale of the FEEBS predicted the perceived strength of forensic evidence. A partial mediation model is presented which explains the relationship between this bias and verdict preferences. The implications of this potential juror bias are discussed in the context of real juries, the CSI Effect (which refers to anecdotal claims that jurors are biased by the popularity of fictional representations of forensic science on television) and peremptory challenges, as well as future research directions.     

The impact of different types of expert scientific testimony on mock jurors’ liability verdicts

Participants in two experiments acted as jurors for a personal-injury case containing different types of expert testimony. In both experiments, the defendant was more likely to obtain a verdict in his favor when his expert presented anecdotal case histories than when the expert presented experimental data. Participants’ liability judgments were correlated with their perceptions of the experts’ credibility (experiments 1 and 2) and were moderated somewhat by their need for cognition and preference for numerical information (experiment 2). The results are discussed in terms of reasoning heuristics such as the base-rate fallacy.     

Forensic identification science evidence since Daubert: Part II--judicial reasoning in decisions to exclude forensic identification evidence on grounds of reliability

Many studies regarding the legal status of forensic science have relied on the U.S. Supreme Court's mandate in Daubert v. Merrell Dow Pharmaceuticals Inc., and its progeny in order to make subsequent recommendations or rebuttals. This paper focuses on a more pragmatic approach to analyzing forensic science's immediate deficiencies by considering a qualitative analysis of actual judicial reasoning where forensic identification evidence has been excluded on reliability grounds since the Daubert precedent. Reliance on general acceptance is becoming insufficient as proof of the admissibility of forensic evidence. The citation of unfounded statistics, error rates and certainties, a failure to document the analytical process or follow standardized procedures, and the existence of observe bias represent some of the concerns that have lead to the exclusion or limitation of forensic identification evidence. Analysis of these reasons may serve to refocus forensic practitioners' testimony, resources, and research toward rectifying shortfalls in these areas.     

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.     

Effects of genetic and environmental explanations of psychopathy and gender on perceptions of criminal behaviors

Genetic/biological evidence is increasingly introduced into courtrooms but findings regarding its impact are mixed. This study integrates research on psychopathy and the use of genetic evidence in legal contexts by considering how information on genetic causal accounts of psychopathy affect perceptions of culpability, recidivism, amenability to treatment, and sentencing severity. Perpetrator gender was examined as a moderator. Two-hundred thirty-eight undergraduates read a hypothetical violent crime vignette and mock expert testimony regarding psychopathy. The testimony included a diagnosis only, or a diagnosis plus genetic or environmental explanations of the etiology of psychopathy. Results indicated that a genetic account of psychopathy was not clearly perceived as aggravating or mitigating such that participants were more lenient in their perceptions of culpability yet more punitive in their sentencing recommendations when perpetrators were described to have genetically-caused psychopathy. An environmental account of psychopathy was mitigating but only for sentencing severity. In addition, although participants were more lenient in sentencing male and female perpetrators when provided with an environmental cause of psychopathy, participants judged male perpetrators most harshly when provided with a genetic cause of psychopathy. Implications of the relations between etiology and gender in legal decision-making are discussed.     

Forensic Confirmation Bias: Do Jurors Discount Examiners Who Were Exposed to Task-Irrelevant Information?*†

Knowledge of task-irrelevant information influences judgments of forensic science evidence and thereby undermines their probative value (i.e., forensic confirmation bias). The current studies tested whether laypeople discount the opinion of a forensic examiner who had a priori knowledge of biasing information (i.e., a defendant's confession) that could have influenced his opinion. In three experiments, laypeople (N = 765) read and evaluated a trial summary which, for some, included testimony from a forensic examiner who was either unaware or aware of the defendant's confession, and either denied or admitted that it could have impacted his opinion. When the examiner admitted that the confession could have influenced his opinion, laypeople generally discounted his testimony, as evidenced by their verdicts and other ratings. However, when the examiner denied being vulnerable to bias, laypeople tended to believe him—and they weighted his testimony as strongly as that of the confession-unaware examiner. In short, laypeople generally failed to recognize the superiority of forensic science judgments made by context-blind examiners, and they instead trusted examiners who claimed to be impervious to bias. As such, our findings highlight the value of implementing context management procedures in forensic laboratories so as not to mislead fact-finders.