11006_The use of filler samples moderates the effect of contextual information on forensic match decisions

Graduate Theses and Dissertations
Iowa State University Capstones, Theses and
Dissertations
2017
The use of filler samples moderates the effect of
contextual information on forensic match decisions
Adele Quigley-McBride
Iowa State University
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Recommended Citation
Quigley-McBride, Adele, “The use of filler samples moderates the effect of contextual information on forensic match decisions”
(2017). Graduate Theses and Dissertations. 15608.
https://lib.dr.iastate.edu/etd/15608

The use of filler samples moderates the effect of contextual information on forensic
match decisions

by

Adele Quigley-McBride

A thesis submitted to the graduate faculty

in partial fulfillment of the requirements for the degree of

MASTER OF SCIENCE

Major: Psychology

Program of Study Committee:
Dr. Gary L. Wells, Major Professor
Dr. Christian A. Meissner
Dr. Stephanie Madon

The student author and the program of study committee are solely responsible for the
content of this thesis. The Graduate College will ensure this thesis is globally accessible and
will not permit alterations after a degree is conferred.

Iowa State University

Ames, Iowa

2017

Copyright © Adele Quigley-McBride, 2017. All rights reserved.
ii

TABLE OF CONTENTS

Page
LIST OF FIGURES ………………………………………………………………………………………
iv
LIST OF TABLES
………………………………………………………………………………………..
v
ACKNOWLEDGMENTS ……………………………………………………………………………..
vii

ABSTRACT……………………………….
…………………………………………………….. viii
CHAPTER 1
INTRODUCTION ………………………………………………………………..
1
The Problem of Contextual Bias in Forensic Contexts
………………………………….
1

How Contextual Information Influences Judgments …………………………………….
2

Current Research Addressing Forensic Contextual Bias ……………………………….
5
Is There a Solution to the Problem of Contextual Bias in Forensic Examination?
7
Evidence Lineups Versus Evidence Showups ……………………………………………..
8
Predictions Based on Eyewitness Identification and Contextual Bias Literatures 10

CHAPTER 2
METHOD ……………………………………………………………………………
14

Participants and Design
…………………………………………………………………………….
14

Materials
……………………………………………………………………………………………
14

Procedure
……………………………………………………………………………………………
17
CHAPTER 3
RESULTS ……………………………………………………………………………
20

Overview of Analyses
………………………………………………………………………………
20

Overview of Results
…………………………………………………………………………………
21

Analysis of the Full Multilevel Model
………………………………………………………..
23

Was There a Contextual Bias Effect in the Standard Procedure?
……………………
24

Was There a Contextual Bias Effect in the Filler-Control Procedure?
…………….
26

Does the Filler-Control Procedure Decrease “False Alarms” Compared

With the Standard Procedure? …………………………………………………………………..
28
Does the Filler-Control Procedure Reduce the Number of Correct
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Match Decisions Compared with the Standard Procedure?
……………………………
29
Does the Filler-Control Procedure Result in Better, Applied Outcomes? ………..
31
Is the Increase in d´ from the Filler-Control Procedure due to
Differential Filler Siphoning? ……………………………………………………………………
34
Are the Contextual Bias Effects and the Effect of the Filler-Control
Procedure Reflected in the Confidence Measures? ………………………………………
37

CHAPTER 4
DISCUSSION ………………………………………………………………………
39

REFERENCES …………………………………………………………………………………………….
49
APPENDIX A
FINGERPRINT SETS …………………………………………………………..
62
APPENDIX B INSTRUCTIONS
…………………………………………………………………
94
APPENDIX C CONTEXTUAL BIAS MATERIALS …………………………………….
95
APPENDIX D IRB ETHICS APPROVAL …………………………………………………… 103

iv

LIST OF FIGURES

Page

Figure 1 A graphical representation of the multilevel logistic
regression models that used binary sample choice variables as
the dependent measure, with three predictors, and two higher
level grouping variables ……………………………………………………………………
54

Figure 2 A graphical representation of the multilevel model
used in the analyses with participant’s confidence in their decisions
as the dependent measure. …………………………………………………………………
55

v

LIST OF TABLES

Page
Table 1 A table summarizing of the number of participants
in each between-subjects condition …………………………………………………….
56
Table 2 Summary of the mean proportion of people in each
between-subjects condition who selected match or no match,
and the mean confidence for each decision in the pilot data …………………..
56
Table 3 A summary of the terminology for the dependent
measures in the logistic multilevel regression analyses. ………………………..
56
Table 4 Summary of the mean proportion of people in each
between-subjects condition who selected match or no match.
………………..
57
Table 5 Summary of the mean proportion of people in each
between-subjects condition who selected match or no match,
separated by ambiguity condition
……………………………………………………….
57
Table 6 Summary of the mean confidence level of people in
each between-subjects condition who selected match or no match,
separated by procedure and context presence ………………………………………
58
Table 7 Summary of the mean confidence level of people in each
between-subjects condition who selected match or no match,
separated by procedure, ambiguity condition, and context presence ……….
58
Table 8 Table comparing the d´ values in each procedure, with
and without context, with all fingerprint materials, and then
separated by ambiguity condition
……………………………………………………….
59
Table 9 Table showing the intraclass correlation (ICC) values
for Fingerprint Set and Participant grouping variables in the current data.
59
Table 10 A summary of the multilevel models assessing contextual
bias in the data obtained from participants who received the standard
procedure and more ambiguous materials. …………………………………………..
60
Table 11 A summary of the two-level logistic multilevel model results
to assess the affects of predictors on each decision type.
……………………….
60
vi

Table 12 A summary of the two level logistic multilevel model results
to what predictors influence the confidence level participants’
had in their decisions ………………………………………………………………………..
61
Table 13 A summary of the three-way ANOVA with Context Presence,
Ambiguity Level, and Procedure Type as factors with two levels,
and d´ as the outcome variable. ………………………………………………………….
61

vii

ACKNOWLEDGMENTS

I would like to thank my advisor, Dr. Gary Wells, and my committee members, Dr.
Christian Meissner, and Dr. Stephanie Madon, for their guidance and support throughout the
course of this research. I would also like to thank Dr. Andrew Smith for his help planning
and analyzing this project. Finally, I would like to thank all of the research assistants who
helped to run these experiments, and those who took the time to participate in my experiment
for course credit.
In addition, I would like to thank my partner, Johnie Allen, and my good friends here
at Iowa State University—Kimberley More, Curt More, Nicole Hayes, Rachel Dianiska, and
Dominick Atkinson—for their constant encouragement, offering advice, listening to my
crazy research ideas, and being there when I need some excitement or relaxation. Finally, I
would like to thank my parents, Dr. Neil Quigley and Norine McBride, and my brothers,
Robert and Ian, for putting up with my nonsense and for Skyping me all the way from New
Zealand to remind me that I’ve always been a smarty-pants and a know-it-all and, therefore,
built for graduate school.

viii

ABSTRACT
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
ix

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.
Keywords: forensics, fingerprints, contextual bias, heuristics, lineups, filler-control
method, evidence lineups.

1
CHAPTER 1. INTRODUCTION
Lana Canen was charged with murder in 2004. The main evidence supporting her
conviction was a latent fingerprint analysis matching her fingerprints to prints found at the
crime scene. A local detective with minimal training in fingerprint examination performed
the analysis and testified that her prints matched those found at the crime scene. This,
combined with confession evidence from another man implicating her as his accomplice,
lead to her eight-year imprisonment for a crime she did not commit. On appeal, the
fingerprints were re-examined and it was discovered that they did not match—even the
original examiner agreed that the prints did not match when the original examiner was
allowed to re-analyze the prints (CBS News, 2012). How does a mistake like this occur? We
know that the criminal justice system is fallible, but law enforcement professionals and the
public view forensic science as reliable and credible. The Innocence Project (Innocence
Project, 2016) has exonerated 330 people who were wrongfully convicted and, of these, 155
have involved some form of forensic examination error. Furthermore, these numbers only
represent the cases that have been found and resolved—the problem is likely much more
prevalent (Charman, 2013). There is a need for a systematic investigation of forensic
techniques and potential solutions to the errors seen in forensic examination.
The Problem of Contextual Bias in Forensic Contexts
The National Academy of Sciences (2009) released a report highlighting the need for
more research into forensic examination error rates, their causes, and how to prevent error in
forensic science. Of particular concern in the National Academy report was the impact of
confirmation bias and contextual bias on forensic analysis, which the current study seeks to
address. There is already some literature that speaks to the nature of contextual bias effects

2
and how they arise. To date, most of the empirical research seeking to find a solution to
contextual bias has focused on finding the conditions under which contextual bias occurs,
and then attempting to shield examiners from contextual information (Dror, Peron, Hind, &
Charlton, 2005) or control when the contextual information is revealed (Dror et al., 2015;
Dror, 2016). The current work, in contrast, assumes that it is almost impossible to fully shield
forensic examiners from contextual information and therefore examines a method for
neutralizing or diluting the impact of contextual information for a class of forensic tests that
constitute “match” or “source” tests. In a match or source test, the examiner is typically
presented with a crime scene sample (e.g., a latent fingerprint, fibers, shoeprint) and a
suspect sample (prints from the suspect, fibers associated with the suspect, shoes of the
suspect) and asked if the suspect sample was the source for the crime sample or if they
“match.” The current study used fingerprints, but the same general principles and findings
should apply to other source or match tests as well.
How Contextual Information Influences Judgments
So, what does the literature tell us about why contextual information might bias
examiners to think that two fingerprints look alike when they are not? The answer lies in
ordinary cognition and decision-making processes. When people make decisions, two kinds
of cognitive processing are used. Bottom-up processing is a data-driven analysis where
details of a stimulus are analyzed in a systematic way, without drawing on any other
information (Chaiken & Maheswaran, 1994). For example, fingerprint examiners use
bottom-up processing when they analyze the pattern of ridges and pores in a fingerprint to
compare to another fingerprint.

3
But bottom-up processing is most useful when the stimuli provided are unambiguous
and there is sufficient time to undergo a detailed analysis of all the material available. As a
result, people often rely on top-down processing or heuristics—making a judgment based the
likelihood of each potential outcome when the resources available are inconclusive (Chaiken
& Maheswaran, 1994; Saks, Risinger, Rosenthal, & Thompson, 2003). Lack of a clear
answer is not the only reason why someone might start to rely on top-down processing, but
these conditions will push people towards heuristic processing. One way heuristics can
operate is by using prior knowledge, beliefs, or expectations to form a base-rate—an idea
about the relative frequency of an outcome within a given set of circumstances (Tversky &
Kahneman, 1974). This kind of processing occurs in situations of uncertainty, when the
available resources are limited, unclear, or there are time constraints, such as a rushed
analysis of a partial fingerprint (Dror, et al., 2005; Neth & Gigerenzer, 2015).
Heuristics can be most helpful in ambiguous situations and heuristics often lead to
efficient and accurate decision-making for everyday situations (Neth & Gigerenzer, 2015).
But, heuristics can also result in biased or erroneous decisions. For example, if the other
information we draw on to help inform our judgment is inaccurate; our final decision might
also be inaccurate. If people look for evidence to support an expected outcome and ignore the
evidence against that outcome, our final decisions will be biased towards our expectations
(confirmation and contextual bias; Einhorn & Hogarth, 1981; Saks et al., 2003; Tversky &
Kahneman, 1974). Contextual bias in a forensic setting can take on many forms, because
there are many kinds of information that can be interpreted as incriminating. Maybe the
examiner saw the crime described in the paper, with all the evidence against the suspect
described in detail, or the examiner saw the press conference put together by the police on

4
television. What if the examiner overheard at the local hangout after work that the suspect
tried to flee when they were approached initially for questioning? Or maybe the police officer
that brings the evidence to the examiner is highly respected and is fairly sure “this is their
guy”.
To make this idea more concrete, think about the case of Lana Canen again. When the
examiner performed the analysis of the fingerprints, he knew that another person had
confessed and named her as his accomplice. So, the examiner probably did not begin the
examination with a neutral starting point, open to being swayed equally by incriminating or
exculpatory evidence. Rather, the examiner likely began the examination with the
expectation that the prints would probably match, an expectation that could have been guided
by the contextual information about the confession. Subsequently, he might have been more
likely to look for aspects of the prints that confirmed his expectation, and ignore the aspects
of the prints that disconfirmed. In addition, much more disconfirming evidence would have
been required to override the examiner’s expectation that the prints should match once the
examiner had formed the idea (Nickerson, 1998). Expectations can be formed by any number
of different sources—police case reports, communication with police, and media can all
change a fingerprint examiner’s view about the likelihood that a set of prints should match.
This is problematic for the presentation of forensic evidence in court. Forensic
experts are hired to testify about their analysis of the prints using the bottom-up process only.
They are not hired to evaluate the credibility of a confession, the suspicions of the police
investigator, a media slant, or interpret suspect behavior. These are all aspects of the case that
will be analyzed and, if admissible, presented in court by people with that expertise, such as
psychologists, police investigators, and interrogators. If the forensic analyst uses contextual

5
information available to them to inform their decision, their testimony in court may involve
double counting of evidence or be based on inaccurate or inadmissible evidence. Of course,
contextual information can be accurate information, so contextual information could help the
examiner make a correct decision. Nevertheless, contextual information is not for the
examiner to weigh; another expert or a direct witness should be the one to present contextual
information in court if it is probative and admissible. Therefore, contextual information does
not need to be, and should not be, allowed to influence the forensic examiner’s evaluation.
So, we need to find a solution to the problem of contextual bias to protect the independence
of forensic expert testimony at trial.
Current Research Addressing Forensic Contextual Bias
There is research demonstrating that contextual bias is a problem in forensic
fingerprint examination, for ordinary people (Dror, Peron, Hind, & Charlton, 2005; Osborne
& Zajac, 2016) and forensic experts (Dror, Charlton, & Peron, 2006). Other forensic
materials have also been used, including handwriting (Kukucka & Kassin, 2014), bitemarks
(Osborne et al., 2014), shoe impressions (Kerstholt, Paahuis, & Sjerps, 2007), and ballistics
(Kerstholt et al., 2010). However, the results of studies using materials other than fingerprints
have been mixed, maybe because forensic techniques with fewer known protocols are more
difficult to manipulate in a way that is appropriate for empirical testing, and replicate with
expert participants.
Dror and colleagues (2005) created a paradigm for testing contextual bias in
fingerprints with lay people. Participants were trained briefly to make fingerprint
comparisons. Then, participants determined whether the fingerprints matched. Sometimes the
fingerprints were ambiguous so whether they matched was very unclear, and sometimes the

6
fingerprints were clearer meaning that people could be more certain that they matched or did
not match. In addition, sometimes participants made the decision with the help of additional,
contextual information, and sometimes there was no extra information. There were four
contextual information conditions: people received no context, photos with low emotion
content (e.g. a hammer), photos with high emotional content (e.g. a bloody crime scene), and
subliminal priming of emotional content paired with high emotion photos. Dror and
colleagues found that participants made significantly more match decisions for pairs of
fingerprints that were accompanied by highly emotional images that suggested incrimination.
However, this pattern was only found when the fingerprints were poor quality, rendering the
decision more ambiguous and uncertain. Similar patterns have been found in more recent
studies with ordinary people making judgments about pairs of fingerprints (Langenburg,
Champod, & Wertheimer, 2009), and in a replication of Dror and colleagues’ study (Osborne
& Zajac, 2016).
There is an obvious concern that arises from using lay people rather than experts and
the concern relates to how comparable the results will be and whether undergraduate data is
generalizable to experts. Experts are better able to discriminate between similar fingerprints
(Thompson & Tangen, 2014), but novice examiners tend to be no better than lay people at
matching fingerprints (Thompson, Tangen, & McCarthy, 2014), and lay people can
discriminate between prints at an above-chance level (Vokey, Tangen, & Cole, 2009).
Although there may be differences between experts and novices in their ability to perform
fingerprint analysis and maybe even differences in contextual bias susceptibility, contextual
bias effects appear to be robust to expertise level. For example, Dror and colleagues (2006)
presented five experts with sets of fingerprints that they had determined were a match in

7
previous cases. However, this time the researchers told the experts that these prints were
from a high profile case involving the FBI and Brandon Mayfield. The experts were familiar
with the case and therefore knew that if the prints were from this case, they should not match.
Dror and colleagues found that only one expert determined the prints to be a match now, as
they had in the past. The remaining experts all said that the prints either did not match now,
or that the crime sample was too degraded to decide. These results also show that contextual
bias can work against finding a match when the context suggests that a match is unlikely.
Dror and Charlton (2006) demonstrated similar results with a different group of
experts, but this time there was a control group where examiners were shielded from
additional contextual information. Expert fingerprint examiners were asked to assess
fingerprint materials from eight past cases. The examiners had judged half of these past cases
as individualizations (they were a match), or exclusions (they were not a match). For the
study, the examiners either received no contextual information (4 cases), context suggesting
the prints should match (Incriminating evidence; 2 cases), or context suggest the prints
should not match (Exculpatory evidence; 2 cases) along with each set of prints. Exculpatory
evidence was found to influence fingerprint experts by making the examiner’s decisions
more conservative. In three cases where the examiners had said the prints matched in the
past, the exculpatory evidence lead to the examiners to conclude that the prints did not match
now, and in one case the examiner said the materials were inconclusive. However, there was
no effect of incriminating evidence on expert decision-making found in this study, and in two
cases the experts made a decision inconsistent with their past determination in the absence of
context. So, inconsistencies can occur even without the influence of context.

8

Is There a Solution to the Problem of Contextual Bias in Forensic Examination?
What have researchers recommended to combat contextual bias in forensic contexts?
In the empirical papers on this issue of forensically-relevant contextual bias, authors have
typically suggested shielding forensic examiners from contextual information (Dror et al.,
2005) or gradually introducing levels of contextual information to examiners (Dror et al.,
2015; Dror, 2016). But an examiner can never be totally insulated from contextual
information. Explicit exposure to contextual information through police communication or
case information included when the evidence is handed over is not the only form of biasing
information. Some forms of contextual information are almost impossible to prevent.
Consider, for example, that forensic examiners are members of the community and are likely
to be exposed to media reports on crimes in their area. Evidence from these cases may end up
on their desk for examination. In addition, forensic experts and police tend to socialize in the
same circles, as well as with each other. In fact, even the presentation of a single sample to
be compared with the crime sample suggests that there is good evidence that the prints from
this person should match the crime print (Wells, Wilford, & Smalarz, 2013).
Evidence Lineups Versus Evidence Showups
In this study, I tested a different type of potential solution to the problem of
contextual bias—one that is designed to moderate the effect of contextual bias, while
accepting that contextual information will always be available to examiners. Instead of
shielding examiners from contextual information, Wells, Wilford, and Smalarz (2013)
proposed the use of evidence lineups as a way to dilute the effect of bias. This idea draws on
the already well-developed research in eyewitness identification that seeks to reduce the

9
chances that innocent people who become suspects in an investigation will be mistakenly
identified by an eyewitness. One of the main ideas to come out of eyewitness research is the
idea that a lineup is more protective of innocent suspects than is a showup (Steblay, Dysart,
Fulero, and Lindsay, 2003). A showup is where an eyewitness is shown a single individual,
who is a suspect, and asked to determine whether they are the culprit. A showup would be
equivalent to the current, standard procedure for forensic examination—the crime sample is
presented with a sample obtained from a single suspect and the examiner is asked to decide if
the samples are a match. A lineup is different from a showup because a lineup embeds the
suspect among other people who, although known to be innocent, fit the description of the
culprit that was obtained from the eyewitness (Wells, 1993). These non-suspect lineup
members are called lineup fillers. So, now the test is not simply whether the eyewitness can
tell if the individual is similar to the culprit, but rather the eyewitness needs to be able to pick
the culprit out of a number of people who could plausibly be the culprit. Importantly, if the
eyewitness picks someone from the lineup who is known to be innocent (a filler), there are
no incriminating consequences of this incorrect identification for the filler. After all, filler are
known-innocents in a lineup.
How would lineups work in a forensic context such as with fingerprints materials? If
the suspect sample is embedded in a lineup of other highly-similar samples, contextual
information still cannot tell the examiner which of the samples is a match to the crime
sample. Although the contextual information can raise expectations that one of the samples
should be a match to the crime sample, contextual information cannot point the examiner to
any one sample if the filler-control method is used. Thus, the examiner cannot simply use the
contextual information and instead must perform a bottom-up analysis of the prints. In fact,

10
an expert examiner may simply decide not to rely on the contextual information at all
because it is largely useless with respect to the task at hand. This aspect of the lineup
procedure is what makes this solution qualitatively different from the other recommendations
that attempt to shield examiners from contextual information. An evidence lineup does not
rely on contextual information being hidden from examiners, or examiners using their
“willpower” to be objective. Instead, the use of fillers should tend to neutralize or dilute the
contextual information due to the fact that the contextual information is not specific to one of
the samples but instead applies to the set of samples as a whole.
To test the viability of the filler-control procedure, I had undergraduate participants
learn about fingerprint examination, and then decide whether a single fingerprint matched a
crime print (standard forensic procedure), or whether one of six fingerprints matched a crime
print (filler-control procedure). Sometimes, the prints were presented with an incriminating
police case report, and sometimes they were not.
Predictions Based on Eyewitness Identification and Contextual Bias Literatures
The first prediction was that the standard (i.e., no fillers) forensic match procedure
would show a contextual bias effect. That is, there would be significantly more affirmative
match decisions made by participants when they received incriminating contextual
information prior to examining the fingerprint materials than when they did not receive such
contextual information. Also, this effect of incriminating contextual information should be
most pronounced when the prints are more ambiguous. Under ambiguous situations the
bottom-up analysis does not give a clear answer, and so people are more susceptible to
influence from top-down processes (Chaiken & Maheswaran, 1994). This pattern of results

11
would conceptually replicate experiments completed by other research laboratories using
fingerprint materials (Dror et al., 2005; Zajac & Osborne, 2016).
A number of additional hypotheses were derived from the eyewitness identification
literature regarding lineups and showups because of their close analogy to the filler-control
procedure and the standard procedure, respectively, in a forensic match test. First, the
eyewitness identification literature shows more affirmative choosing for lineups than for
showups. This is due to the fact that there are more faces that could potentially resemble an
eyewitness’s memory of the culprit when viewing a lineup than when viewing a showup.
Similarly, it was predicted that there would be more affirmative match decisions for the
fingerprint lineup than for the fingerprint showup due to the fact that there are more possible
prints to resemble the latent print.
The eyewitness literature shows, however, that this higher rate of affirmative
responding for lineups than for showups does not result in more mistaken affirmative
responses on the innocent suspect. This is because, although there is more choosing for
lineups because there are more options, the innocent suspect is no longer the only plausible
choice. In fact, there are a number of other fillers that match the description of the culprit as
well. Because the innocent suspect is not actually the culprit and therefore not a great match
to the eyewitness’ memory, choosing will spread out to the fillers, thereby reducing the false
positives on the innocent suspect to a level that is significantly lower than the rate observed
for showups (filler siphoning; Wells, Smalarz, & Smith, 2015; Wells, Smith, & Smalarz,
2015). Fillers will also siphon some positive identifications away from the actual culprit, but
to a lesser extent because the culprit is a good match to memory. This phenomenon is called
differential filler siphoning as the fillers have a differential effect contingent on whether the

12
actual culprit is in the lineup. Good fillers will siphon away from an innocent suspect more
than they will from a guilty suspect, and this is the mechanism through which the ratio of
innocent suspect identifications and actual culprit identifications (as well as d´ values)
improves when lineups are used. Based on this consistent result in the eyewitness literature, it
was predicted that this same differential filler siphoning would occur when comparing
fingerprint lineups to fingerprint showups.
Another hypothesis for the current study was that contextual bias effects would be
diluted in the filler-control procedure when compared to the standard procedure. In effect,
this dilution prediction is closely related to the idea of filler siphoning. For example, if
incriminating contextual information increases false affirmative match decisions by 12%,
then the entire 12% increase would fall on the innocent suspect sample for the standard
(showup type) procedure. For the filler-control procedure, however, the 12% increase in false
affirmative responding that results from incriminating contextual information would dilute
(spread) across the six samples, producing (on average) a mere 2% increase in false
affirmative match decisions on the innocent suspect. An alternative hypothesis was that
contextual information would have little or no effect at all on affirmative match decisions
when using the filler-control method. This is because, although the contextual information
suggests to the examiner that there should be a match, contextual information does not assist
the examiner at all on being able to determine which of the six samples matches the crime
sample. Accordingly, the contextual information does not relieve any of the examiner’s
burden of relying as much as possible on the bottom-up approach. Hence, when given the
fingerprint lineup (rather than the fingerprint showup) the examiner might simply dismiss the

13
contextual information as being irrelevant or unhelpful and rely almost totally on
characteristics of the prints themselves.
Finally, predictions were made about the confidence that the examiners expressed in
their decisions. First, confidence should be overall lower in the filler-control procedure
because the task is more difficult. Furthermore, when people make an incorrect decision,
confidence should be lower compared with when they make a correct decision. This is
expected because there is typically a confidence-accuracy relation seen in eyewitness
identification studies (Wixted & Wells, 2017) as well as other tasks for which people
perform above chance levels. Also, the more ambiguous materials should result in lower
confidence in the decisions too—this hypothesis functions as a manipulation check as well.
Furthermore, when people make a decision that is incongruent with the suggestion in the
contextual information (e.g. the context implies guilt but the participant says there is no
match), confidence should be reduced compared with when the contextual information agrees
with their match decision. Additionally, it was anticipated that there may be stronger
evidence of contextual bias in the confidence measure rather than the binary match decision
because the measure is much more sensitive (scores ranging from 0 to 100% confidence
compared with a two-option forced choice measure).

14
CHAPTER 2. METHOD
Participants and Design
A total of 244 undergraduate participants from a Midwestern University took part in
the study for partial course credit. All participants were fluent English speakers and over the
age of 18 years. Nine participants were excluded from analyses due to experimenter error, or
unusual participant behavior. There were four independent variables in this study: what
procedure was used, whether contextual information was provided, how difficult the task
was, and whether or not one of the samples actually did match the crime sample. The design
was a 2 (context: context vs. no context) x 2 (procedure: standard vs. filler-control method) x
2 (ambiguity: more ambiguous vs. less ambiguous) x 2 (match presence: match present vs.
match absent) mixed factorial model.
Context, procedure, and ambiguity were manipulated between subjects and match
presence manipulated within subjects. Participants were randomly assigned to ambiguity,
procedure, and context conditions, and half of the fingerprints that each participant saw
matched, and half did not, presented in a random order. Refer to Table 1 for a breakdown of
the numbers in the between subjects groups.
Materials
The session began with a training video on fingerprint analysis (Introduction to
Fingerprint Analysis, 8:00), created using information about FBI standards and training for
fingerprint analysis. The video consists of a series of informative Power Point slides with a
voice over and contains information about the background of fingerprint analysis, how an
analysis is performed, and then a number of working examples for the participants.
Participants watched the video on the computer screen with headphones on. The training

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video and response questions were all presented on a desktop computer using MediaLab
software.
The fingerprint samples were from a previous study by Marcon (2009), using
fingerprints from 125 students at the University of Texas at El Paso. There were three
different levels of print quality. Rolled fingerprints include the entire print from the tip of the
finger and are rolled slowly and deliberately from one side of the finger to the other to ensure
the print is clear. Plain fingerprints are not rolled, so they do not include as much detail from
the sides of the finger and can sometimes be unclear or smudged. Partial fingerprints, or
latent fingerprints, occur when someone quickly touches a surface, not attempt to leave a
deliberate print. Partial fingerprints typically lack detail, are smudged, or unclear. Marcon
also had 60 undergraduates rate how distinct and typical each print is from all the other
prints. The final library of fingerprint sets that are rated consists of fingerprints from 113
undergraduates.
Crime scene samples in the more ambiguous condition were drawn from the less clear
plain prints, or partial print samples. In the less ambiguous condition, in contrast, the crime
prints were drawn from rolled or plain prints, and were complete, with sharper lines and no
smudging. Fillers samples for the filler-control procedure were selected based whether they
had the same fingerprint pattern (loop, whorl, or arch) and came from the same finger (index,
thumb, etc). In the more ambiguous condition, the filler samples were also pulled from
partial or less clear plain fingerprint samples, whereas the less ambiguous condition the
fillers are clearer. The fingerprints were selected so that the fingerprints were representative
of the range of typicality and distinctiveness ratings collected by Marcon (2009).