1. The Effect of the Confirmation Bias on Interpretations of Eyewitness Confidence Statements
Sarah Carroll
Faculty Advisor: Chad Dodson
Department of Psychology, University of Virginia
Abstract
Materials & Methods
Results
Participants: 624 adults completed our survey on Amazon Mechanical Turk.
Materials: 8 lineups of black and white faces.
8 statements of confidence: 4 high confidence and 4 moderate confidence
8 justifications (for participants in the Featural and Unobservable Justification conditions)
Procedure: Figure 1 shows the task for the control participants. In each of the 8 lineups, an eyewitness has identified a face, highlighted in red, and provided a verbal expression of confidence. Participants translated this expression into a number using the provided numeric scale (see bottom of Figure 3). Participants either saw a confidence statement alone, as depicted in Figure 1, or a confidence statement followed by either an unobservable (Figure 2) or featural justification (Figure 3).
This study examined the effect of prior beliefs regarding a suspect’s guilt on interpretations of eyewitness statements of confidence.
Individuals often misinterpret eyewitness’ verbal expressions of confidence (e.g., I’m fairly sure it’s him) (Dodson & Dobolyi, 2015).
Participants completed an online survey showcasing 8 police lineups. Each lineup indicated a suspect chosen by the eyewitness and a suspect chosen by the police.
4 lineups: Suspect Confirmed
4 lineups: Suspect Disconfirmed
Participants rated eyewitnesses in the Suspect Confirmed slides as more confident than those in the Suspect Disconfirmed slides, although participants were reminded that the eyewitnesses never knew the identity of the police suspect.
Figures 2 and 3 show the task for the bias participants. Participants saw 8 lineups with the eyewitness’s choice highlighted in red and a police suspect indicated with a "Suspect" watermark. In 4 lineups the police suspect and the eyewitness identification were the same man (figure 2) and in 4 they were different (figure 3).
Figure 1
Figure 2
Introduction
Figure 4
When a detective believes that a particular member of a lineup is guilty, it is unclear whether his belief will affect his interpretation of an eyewitness’s expression of confidence.
Dodson & Dobolyi (2015): participants who saw an eyewitness’s expression of confidence accompanied by a reference to a visible feature of the suspect (e.g., I remember his nose) assumed that the eyewitness was less confident in his identification. In the present study, we varied the type of justification accompanying the lineups.
Individuals tend to interpret and recall information such that it confirms their existing beliefs, a phenomenon known as the confirmation bias (Wason, 1960).
The present research investigates whether such a bias may influence another individual’s understanding of an eyewitness’s confidence statement. 
Lower perceived confidence in Featural condition than Unobservable and Confidence Only conditions
Higher perceived confidence in Suspect Confirmed than Suspect Disconfirmed lineups
Suspect Confirmed vs. Disconfirmed relative to Control
Confidence Only: Comparable increase in Confirmed & decrease in Disconfirmed
Unobservable Justification: Larger decrease in Disconfirmed
Featural Justification: Larger increase in Confirmed
Figure 3
Conclusion
Even though participants understood that the eyewitnesses never knew who the police suspect was, the identity of the suspect affected their beliefs about the eyewitness’ confidence.
The effect of the bias manipulation depended on the Justification condition.
Implication for the justice system
The detective who created the lineup should not interview the eyewitnesses, because his prior beliefs may influence his interpretation of the eyewitness’ testimony.
Hypothesis
Participants will rate the eyewitnesses as more confident in the Suspect Confirmed lineups than in the Suspect Disconfirmed lineups.
References
Dodson, C. S., & Dobolyi, D. G. (2015). Misinterpreting eyewitness expressions of confidence: The featural justification effect. Law and human behavior, 39(3), 266.
Wason, P. C. (1960). On the failure to eliminate hypotheses in a conceptual task. Quarterly journal of experimental psychology, 12(3),