Date of Award
Master of Science
Gary L. Wells
The criminal justice system is susceptible to errors that can lead to wrongful conviction of innocent people, sometimes caused by faulty forensic evidence presented at trial. Among the problems is the fact that contextual information can bias forensic examiners to make “match” decisions when the materials are ambiguous (Dror, Peron, Hind, & Charlton, 2005; Dror, Charlton, & Peron, 2006). It is unlikely that contextual information could ever be eliminated from police investigations and the forensic examination procedure. Instead, the current experiment suggests that providing examiners with evidence lineups—analogous to eyewitness identification lineups where the suspect is embedded among similar-looking, known innocent fillers—can reduce the effect of contextual bias. This paper describes the first experiment conducted to demonstrate the effectiveness of evidence lineups, called the filler-control procedure (Wells, Wilford, & Smalarz, 2013). Participants were trained and then examined eight sets of fingerprint materials. The materials were either more ambiguous or less ambiguous, and some of the sets had an actual match present and some did not. Furthermore, some participants received the filler-control procedure, and some the standard procedure—only one comparison print to compare to the crime print, as is standard in forensic examination procedures. The final manipulation was the presence or absence of related contextual information, in the form of a police case report suggesting that the suspect in the case is guilty. The results showed a contextual bias effect in the standard procedure when the materials were more ambiguous, but only when there was no actual fingerprint match present. So, the innocent suspect is in the most danger when the materials are degraded or difficult to compare, and the innocent suspect’s print is the only print presented to compare to the crime sample. The filler-control procedure, however, eliminated the effect of contextual information. Although the number of affirmative match decisions increased when using the filler-control method, these match decisions were spread across the lineup to the filler prints rather than loading onto the innocent suspect. These results mirror the results found in eyewitness identification, and show promise for use in the real world as a means to reduce wrongful conviction and improve forensic testing accuracy.
Quigley-McBride, Adele, "The use of filler samples moderates the effect of contextual information on forensic match decisions" (2017). Graduate Theses and Dissertations. 15608.