Eyewitnesses' Free-Report Verbal Confidence Statements Are Diagnostic of Accuracy

• Published in: Law and human behavior 2021-04, Vol.45 (2), p.138-151
• Main Authors: Smalarz, Laura, Yang, Yueran, Wells, Gary L.
• Format: Article
• Language: English
• Subjects: Female; Human; Human Information Storage; Male; Memory; Policy Making; Self-Confidence; Verbal Memory; Videotapes; Witnesses
• ISSN: 0147-7307; 1573-661X
• DOI: 10.1037/lhb0000444

Objectives: We assessed recent policy recommendations to collect eyewitnesses' confidence statements in witnesses' own words as opposed to numerically. We conducted an experiment to test whether eyewitnesses' free-report verbal confidence statements are as diagnostic of eyewitness accuracy as their numeric confidence statements and whether the diagnostic utility of eyewitnesses' verbal and numeric confidence statements varies across witnessing conditions. Hypotheses: We hypothesized that eyewitnesses' verbal and numeric confidence statements are both significantly associated with identification accuracy among choosers and that their diagnostic utility holds across varying witnessing conditions. Method: In the first phase of the experiment, eyewitnesses (N = 4,795 MTurkers; 48.8% female; 50.8% male; .3% other; age M = 36.9) viewed a videotaped mock-crime and made an identification decision from a culprit-present or culprit-absent lineup. We manipulated witnessing conditions at encoding and retrieval to obtain varied levels of memory performance. In the second phase of the experiment, evaluators (N = 456 MTurkers; 35.5% female; 62.7% male .4% other; age M = 36.5) translated witnesses' verbal confidence statements to a numeric estimate and we used calibration and confidence-accuracy characteristic analyses to compare the diagnosticity of witnesses' verbal and numeric confidence statements across the two levels of memory performance. Results: Witnesses' verbal and numeric confidence statements were significantly and nondifferentially diagnostic of eyewitness accuracy for both choosers and nonchoosers, and their diagnostic utility held across variations in witnessing conditions. Conclusions: These findings suggest the applied utility of collecting either verbal or numeric confidence statements from eyewitnesses immediately following an identification decision. Public Significance StatementLegal practitioners such as police, attorneys, judges, and jurors must make determinations about the accuracy of eyewitnesses' identifications of criminal suspects based on the level of confidence expressed by eyewitnesses. This research demonstrated that both numeric (e.g., "I'm 95% confident") and verbal (e.g., "I'm absolutely sure") confidence statements, collected using best-practices, provide diagnostic information about eyewitness accuracy.