Objective: We investigated the impact of eyewitness confidence on the following dependent variables: (a) guilty or not-guilty verdict; (b) judgments of guilt as measured on a scale; and (c) mock jurors' perception of the accuracy of an eyewitness's identification. In addition, we examined two potential moderators of the effects of eyewitness confidence: (a) whether the eyewitness expressed confidence at trial versus during the initial lineup identification and (b) whether the eyewitness provided a numerical versus a verbal statement of confidence. Hypotheses: We expected all analyses to reveal that highly confident eyewitnesses are more persuasive to mock jurors than are eyewitnesses with lower confidence (Hypothesis 1). We expected eyewitness confidence at trial (relative to at identification) to be more persuasive to mock jurors (Hypothesis 2). We expected numerical expressions of confidence to be more persuasive to mock jurors than verbal confidence expressions (Hypothesis 3). Method: We conducted a meta-analysis of 35 studies from 20 published papers and seven theses or dissertations to quantify the effect of eyewitness confidence on juror judgments and investigated the influence of two primary moderator variables, time of confidence and format of confidence expression. Results: All analyses revealed an effect of eyewitness confidence on mock juror decisions (gs = .21-.36). Our moderator analysis showed that the timing of the confidence statement (identification vs. trial) did not affect the influence of eyewitness confidence on mock jurors' judgments of guilt or accuracy. The influence of eyewitness confidence was not moderated by verbal versus numerical expressions of confidence. Conclusions: Although eyewitness confidence is persuasive to mock jurors, the size of this effect is modest. Moreover, verbal and numerical expressions of confidence have similar persuasive effects, and mock jurors do not appear to be sensitive to the likely difference in evidentiary strength of eyewitness confidence expressed at the initial identification versus at trial. Public Significance StatementHighly confident eyewitnesses are persuasive to jurors, but eyewitness misidentification is a leading cause of wrongful imprisonment. Although confidence at the time of an initial identification from a lineup can be predictive of eyewitnesses' accuracy, confidence at trial is typically not. Our findings suggest that mock jurors are not sensitive to this distinction and that they weigh eyewitness confidence at trial as strongly as they weigh confidence at the time of the identification. Understanding how jurors weigh eyewitness confidence from these two time points can promote new ways of instructing jurors to properly assess eyewitness testimony.
Are jurors more likely to convict a suspect who has been identified by multiple eyewitnesses than by a single one? Participants saw a lineup of faces with one face highlighted as having been identified by either one or two highly confident eyewitnesses. Participants estimated the likely guilt of the suspect. Two eyewitnesses were not more persuasive than one when either the single or the multiple eyewitnesses had provided a featural justification about their identification (e.g., "I remember his eyes"). But, guilt judgments were reliably higher in the two eyewitness than in the single eyewitness condition when eyewitnesses provided either a confidence statement only or a confidence statement with a recognition justification (e.g., "I recognize him"). Furthermore, two eyewitnesses who mention different features are less persuasive than two eyewitnesses who mention the same feature. The results are consistent with our perceived diagnosticity account.
When an eyewitness makes an identification from a lineup, police are also instructed to collect a verbal expression of confidence. This recommendation hinges on the assumption that evaluators will perceive confidence in the manner the witness intended. However, research has consistently shown that these interpretations can be biased by accompanying contextual information. For example, statements that reference facial features (e.g., “I’m very sure. I remember his eyes.”) are perceived as less confident than when the statement is presented alone (“I’m very sure.”) (featural justification effect). Additionally, perceptions of witness confidence are altered when the witness’s identification (mis-)matches the police suspect in a lineup (prior knowledge). We find that the same underlying mechanism explains the bias induced by both featural justification (Experiments 1 and 2) and prior knowledge (Experiment 3) manipulations. Evaluators conflate their own beliefs about the accuracy of an identification with the witness’s intended level of confidence. A simple warning that highlights the differences between confidence and accuracy eliminates the featural justification effect, but is less effective for mitigating the influence of prior knowledge. The key takeaway from this paper is that distinguishing perceptions of certainty from those of accuracy improves the interpretation of verbal confidence statements.
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