Improving the Interpretation of Verbal Eyewitness Confidence Statements by Distinguishing Perceptions of Certainty From Those of Accuracy

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. Public Significance Statement Police are instructed to collect an eyewitness's confidence in a lineup identification "in [their] own words." People often misinterpret the level of confidence the witness intended to convey when there is information that affects evaluators' perceptions of the witness's accuracy. The key takeaway from this paper is that distinguishing perceptions of certainty from those of accuracy improves the interpretation of verbal confidence statements.