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.     

Science in the Jury Box: Jurors’ Comprehension of Mitochondrial DNA Evidence

Questions about how jurors understand and apply scientific evidence were addressed in a mock jury study in which 480 jury pool members watched a videotaped mock trial that included expert testimony about mitochondrial DNA (mtDNA) evidence purportedly linking a defendant to a crime. Collectively, jurors showed moderately good comprehension of the mtDNA evidence, although some made definitional and inferential errors. Comprehension was better among jurors with higher educational attainment and more mathematics and science courses. Lower comprehension was associated with jurors’ reservations about science and concerns about the contamination of mtDNA evidence. The results suggest that most jurors are capable of comprehending and employing scientific evidence presented during trial, although errors and doubts about the evidence should be anticipated.     

Perceived infallibility of detection dog evidence: implications for juror decision-making

This study focuses on the trust that potential jurors have in unsubstantiated evidence and the implications of such trust for legal decision-making. We examined whether participants’ motivation to think deeply (‘need for cognition,’ NC) and belief in science moderated their trust in potentially fallible detection dog evidence when selecting a verdict in a trial scenario. A detection dog twice indicated the presence of drugs in the scenario, yet no drugs were actually found. Those who chose a guilty verdict without drugs present featured stronger beliefs in detection dog evidence. They were also more confident that a dog alert indicated the presence of drugs, even though the scientific literature actually shows that detection dog evidence is subject to biases and other challenges to reliability. Our findings indicate that an unsubstantiated belief and trust in detection dog evidence may negatively influence juror decision-making, which may, in turn, pose consequences for fairness and justice. Participants believed that detection dogs provide powerful and reliable evidence, and these beliefs were clearly associated with stronger beliefs in science. These findings, therefore, raise serious concerns about jurors’ indiscriminate trust in forensic evidence, be it detection dog evidence or other lines of evidence presented in court.     

Construing Motive in Videotaped Killings: The Role of Jurors' Attitudes Toward the Death Penalty

Death-qualified jurors are generally able to impose the death penalty, whereas excludable jurors are generally either unable or unwilling to do so. A long line of research studies has shown that the former are more likely than the latter to convict criminal defendants. Ellsworth (1993) argues that jurors' attitudes toward the death penalty predict verdicts because they are embedded in a cluster of beliefs and theories about the criminal justice system. Her studies show that jurors interpret ambiguous conduct based on these belief structures. The present study examines the possibility that death penalty attitudes also influence jurors' conceptions of criminal intent. We showed mock jurors the filmed murder of a convenience store clerk and examined the inferences they drew from this evidence. Jurors who favored the death penalty tended to read criminal intent into the defendant's actions and jurors who opposed the death penalty were less likely to do so. These data provide further explanation of the conviction-proneness of death-qualified jurors.     

Understanding juror perceptions of forensic evidence: investigating the impact of case context on perceptions of forensic evidence strength

The most widely accepted model of juror decision making acknowledges the importance of both the case-specific information presented in the courtroom, as well as the prior general knowledge and beliefs held by each juror. The studies presented in this paper investigated whether mock jurors could differentiate between evidence of varying strengths in the absence of case information and then followed on to determine the influence that case context (and therefore the story model) has on judgments made about the strength of forensic DNA evidence. The results illustrated that mock jurors correctly identified various strengths of evidence when it was not presented with case information; however, the perceived strength of evidence was significantly inflated when presented in the context of a criminal case, particularly when the evidence was of a weak or ambiguous standard. These findings are discussed in relation to the story model, and the potential implications for real juries.     

Who do you believe? Assessing student and community member perceptions of bystander and victim witnesses

ABSTRACT

Eyewitness identifications provide critical evidence as they are often persuasive to jurors, but documented misidentifications have led to wrongful convictions . Researchers have examined how jurors evaluate multiple eyewitnesses, but not different types of eyewitnesses, such as bystanders and victims. Additionally, none of this research has examined jurors’ ability to evaluate bystander and victim identifications that vary in quality. Two studies examined student and community members’ perceptions of bystander and victim witnesses. Study 1 participants read about a good or poor-quality identification made by a bystander or victim. Study 2 participants read about both bystander and victim identifications that varied in quality. Both studies found jurors were sensitive to identification quality as demonstrated by a variety of legal decisions, including verdict, though the quality of a second identification in Study 2 did not change any legal decisions. Multiple differences between student and community member samples emerged across both studies suggesting that community members are more likely to trust witnesses and convict. Reliance on student samples may overestimate jurors’ ability to evaluate multiple eyewitnesses and underestimate the likelihood of conviction based on flawed eyewitness evidence.     

Perceptions of older adult jurors: the influence of aging stereotypes and jury laws

ABSTRACT

The present study examined younger (18–30 years, N?=?100) and older adults’ (66–89 years, N?=?100) responses to a jury duty questionnaire assessing perceptions of jury duty, their capability to serve, and the capability of older adults to serve. We also explored perceptions of the senior jury opt-out law (a law that allows those over a certain age (e.g. 65 years) to opt-out of jury duty). We assessed why participants believe this law is in place and experimentally examined if informing older adults about this law impacted their jury questionnaire responses. Results demonstrated that older adults were significantly more likely to want to serve compared to younger adults; however, younger adults provided lower capability ratings of older adult jurors compared to older adults. Younger adults’ open-ended explanations for these ratings indicated negative aging stereotypes (i.e. in part, believing that older adult jurors are less capable because of declining health and biased beliefs). Older adults also had a significantly lower rate of agreement with the senior jury opt-out law. Although informing older adults about this law did not impact their perceptions of themselves as potential jurors, it did enforce more negative attitudes towards older adult jurors as a whole.     

The Effect of Jury Deliberations on Jurors' Reasoning Skills

The effect of jury deliberation on jurors' reasoning skill in a murder trial was examined. Specifically, the effect of deliberating on reasoning competence (as defined by Kuhn, Weinstock and Flaton, 1994) was explored. One hundred and four participants viewed a videotaped murder trial and either deliberated in 12-person juries or ruminated on the case individually. Among those assigned to juries, half had their reasoning skill assessed prior to deliberations, while the others were tested after deliberating. Jurors in the individual rumination condition were assessed after they had the opportunity to reflect on the case alone. As hypothesized, post-group-deliberation jurors were more likely to discount both the selected verdict and alternative theories and incorporate judgmental supporting statements than were the other mock jurors. However, the mock jurors did not differ with regard to making statements that supported alternative verdicts or including judgmental statements that discounted their chosen verdict. In terms of Kuhn's reasoning continuum from satisficing (low level) to theory–evidence coordination (high level), there is some evidence that post-group-deliberation jurors may be closer to the high end than predeliberation jurors or post-individual-rumination jurors in some aspects of the task, but not in others.     

The role of neurological and psychological explanations in legal judgments of psychopathic wrongdoers

Although brain imaging has recently taken center stage in criminal legal proceedings, little is known about how neuroscience information differentially affects people’s judgments about criminal behavior. In two studies of community participants (N = 1161), we examined how mock jurors sentence a fictional psychopathic defendant when presented with neurological or psychological research of equal or ambiguous scientific validity. Across two studies, we (a) found that including images of the brain did not alter mock jurors’ sentencing judgments, (b) reported two striking non-replications of previous findings that mock jurors recommend less severe punishments to defendants when a neuroscientific explanations are proffered, and (c) found that participants rated a psychopathic individual as more likely to benefit from treatment and less dangerous when a neurological explanation for his deficits was provided. Overall, these results suggest that neuroscience information provided by psychiatrists in hypothetical criminal situations may not broadly transform mock jurors’ intuitions about a psychopathic defendant’s sentence, but they provide novel evidence that brain-based information may influence people’s judgments about treatability and dangerousness.     

Taking the bait: interrogation questions about hypothetical evidence may inflate perceptions of guilt

ABSTRACT

During suspect interviews, police will sometimes ask about hypothetical incriminating evidence to evoke a cue to deception – a technique known as a bait question. Previous research has demonstrated such questions can distort peoples’ memory for what evidence exists in a case. Here, we investigate whether such memory distortion can also cause people to see the suspect as more likely to be guilty. Across three experiments, we find exposure to bait questions led to participants hold inflated views of a suspect’s guilt. Further, we demonstrate bait questions cause reliable, robust memory distortion, leading participants to believe non-existent, incriminating evidence exists. However, we found no evidence to support the speculated mechanisms for this inflation – namely, (1) that source monitoring errors could lead people to misremember false evidence as real evidence and (2) that bait questions provide ‘key evidence’ to fill in the gaps of an incomplete theory of a case. In sum, bait questions have the problematic potential to shift jurors towards guilty verdicts. We suggest future research directions on bait questions, including the need for different designs to clarify why bait questions inflate guilt, and recommend practitioners avoid the use of bait questions.     

Do Jurors “Know” What Isn’t So About Child Witnesses?

Are expert witnesses needed in child sexual abuse cases to educate jurors about children’s memory, suggestibility, and reactions to abuse, or do jurors already know what such experts could tell them? To cast light on this question, we surveyed jurors and jury-eligible college students and compared their beliefs with what is known via scientific research regarding children’s memory and ability to testify, reactions to interrogation, and reactions to sexual abuse. We also asked participants to infer results of four widely cited studies of children’s suggestibility. Participants’ beliefs were consistent with findings from research on some issues (e.g., that children can be led to claim that false events occurred) but diverged from the scientific consensus on other issues (e.g., whether children can remember painful events in infancy). Similarly, participants sometimes overestimated and sometimes underestimated the level of suggestibility observed in empirical studies. Individual differences in accuracy were related to participants’ gender, education and ethnicity, and there was considerable disagreement among participants on many questions. Implications of findings for the admissibility of expert testimony in child abuse cases are discussed.     

The Effects of British and American Trial Procedures on the Quality of Juror Decision-Making

Compared to American trial procedures, British procedures provide a less distracting environment in which jurors can process trial evidence. Relying on theories of persuasion, it was predicted that jurors viewing British procedures would be less affected by extra-evidentiary cues and would be more sensitive to evidence strength variations than jurors in American trials. Participants (N = 245) viewed a mock trial in which trial procedure, judge's nonverbal behavior, and evidence strength were varied. Participants judged the British procedures to be more civil and fair than American procedures but were less likely to find for the plaintiff. Although jurors recalled more trial facts when they viewed British procedures, they were not more sensitive to variations in evidence strength. There was some evidence that British procedures may increase the influence of judge's nonverbal behavior on juror judgments. The relative benefits of different trial procedures are discussed.     

Validity Beliefs and Ideology Can Influence Legal Case Judgments Differently

Jurors sometimes enter a case both with prior beliefs about its likely validity and with more general ideologies that are relevant to the case. Although prior validity beliefs may serve as heuristics, directly biasing decisions when cognitive capacity is low, we hypothesized that ideology may bias systematic thought even when cognitive capacity is high. This experiment studied simulated individual juror decisions in a sex-discrimination case, measuring validity beliefs about such cases as well as feminist ideology, and exposing participants to 1 of 3 case versions under time pressure or no time pressure. Validity beliefs had a direct, heuristic impact on judgment only under time pressure. However, feminist ideology had a mediated influence on judgment via valenced thoughts about the evidence, even under no time pressure. Also, people with initially proplaintiff beliefs judged a woman's sex-discrimination suit more negatively than did prodefendants if the evidence was weak. The results suggest that when jurors can fully process information, validity expectancies might backfire if not supported by case evidence, but ideology can have a more pervasive influence on the decision-making process.     

Real jurors' understanding of the law in real cases

A survey of 224 Michigan citizens called for jury duty over a 2-month period was conducted to assess the jurors' comprehension of the law they had been given in the judges' instructions. Citizens who served as jurors were compared with a base line of those who were called for duty but not selected to serve, and with those who served on different kinds of cases. Consistent with previous studies of mock jurors, this study found that actual jurors understand fewer than half of the instructions they receive at trial. Subjects who received judges' instructions performed significantly better than uninstructed subjects on questions about the procedural law, but no better on questions about the substantive (criminal) law. Additionally, jurors who asked for help from the judge understood the instructions better than other jurors. Since the results replicate previous research using simulated trials, this study provides evidence for the generalizability of earlier work to actual trials.     

Mock jurors’ perceptions of a child witness: the impact of the presence and/or intervention of a registered intermediary during cross-examination

ABSTRACT

In recent years Registered Intermediaries (RIs) have been involved in facilitating communication in children's investigative interviews and trial proceedings. Their presence and interventions are generally deemed to have a positive impact on child engagement, but their impact on jury appraisal of evidence, during cross-examination is unclear. This study addressed this issue in a more ecologically valid context than that previously used. Adult mock juror participants (N?=?217) watched a video-recording of a mock cross-examination of a child witness in which a RI was present or absent, and in which RI type interventions were either included or omitted. The participants rated the quality of the cross-examination and the child's responses in relation to child credibility, child understanding, legal professional's behaviour, and trial progression. Findings indicated that RI presence or absence, and inclusion or omission of interventions had no effect on mock juror ratings. However, an interaction between these variables demonstrated that mock jurors rated trial progression towards a guilty verdict according to which court professional did, or did, not intervene. The findings also demonstrated that mock jurors based their assessment of trial progression towards a guilty verdict on the evidence presented, and that child understanding per se was irrelevant.     

The effect of ambiguous question wording on jurors’ presumption of innocence

ABSTRACT

Research suggests that jurors misunderstand the presumption of innocence. However, past studies have not asked participants to estimate the defendant’s probability of guilt, setting aside the fact of charge and indictment. We conduct two studies to explore the impact of this question wording on estimates of the probability of guilt/innocence by jury-eligible Mturk workers. In Experiment 1 (N?=?275), question wording (legal, factual and ambiguous) was varied within participants and revealed significantly higher estimates of innocence in response to the legal than the factual or ambiguously worded question. In Experiment 2 (N?=?303), question wording was manipulated between participants both before (prior) and after (posterior) the presentation of evidence. Prior estimates of guilt were significantly lower in the legal than factual or ambiguous conditions. Question wording also predicted posteriors, and these in turn predicted verdicts. These results suggest that imprecise wording may have contributed to concerns about jurors’ understanding of the presumption of innocence, highlighting the need for further research. Link to associated OSF page: [https://osf.io/ywuxr/?view_only=b2148ffd1f674e62b66d31ed6593e586].