Graduate Theses and Dissertations
Iowa State University Capstones, Theses and
Dissertations
2018
Belief perseverance: The staying power of
confession evidence
Curt More
Iowa State University
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https://lib.dr.iastate.edu/etd/16421
Belief perseverance: The staying power of confession evidence
by
Curt Craig More
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:
Stephanie Madon, Co-Major Professor
Max Guyll, Co-Major Professor
Marcus Credé
The student author, whose presentation of the scholarship herein was approved by the program
of study committee, is 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
2018
Copyright © Curt Craig More, 2018. All rights reserved.
ii
DEDICATION
This thesis is dedicated to my family. To my wife, Kimberly More, for her love and
encouragement. To my parents, Susan More, Bruce More, and Joseph Kitzke, for their support,
both emotional and financial. To the grandparents I have lost, Kay Brayshaw, Joe Kitzke, and
George More, for their unconditional love. And to the grandparents I still have, Don Brayshaw,
Evona Kitzke, and Pat More, for their unwavering love and belief in me.
iii
TABLE OF CONTENTS
Page
LIST OF FIGURES ………………………………………………………………………………………
v
LIST OF TABLES
………………………………………………………………………………………..
vi
ACKNOWLEDGMENTS ……………………………………………………………………………..
vii
ABSTRACT……………………………….
…………………………………………………….. viii
CHAPTER 1. INTRODUCTION ……………………………………………………………………
1
Error and Bias …………………………………………………………………………………………
2
Belief Perseverance
………………………………………………………………………………….
3
The Power of Confession Evidence
……………………………………………………………
5
Ambiguity …………………………………………………………………………………………
7
Commitment ……………………………………………………………………………………..
7
Research Overview and Hypotheses
…………………………………………………………..
8
CHAPTER 2. METHOD ……………………………………………………………………………….
10
Power Analysis ……………………………………………………………………………………….
10
Participants
……………………………………………………………………………………………..
10
Design ……………………………………………………………………………………………………
11
Crime Report
…………………………………………………………………………………………..
11
Measures ………………………………………………………………………………………………..
12
Guilt Judgments …………………………………………………………………………………
12
Perceptions of Impartiality
…………………………………………………………………..
12
Manipulation Check
……………………………………………………………………………
12
Attention Check …………………………………………………………………………………
13
Suspicion Check
…………………………………………………………………………………
13
Scrambled Anagrams ………………………………………………………………………….
14
Procedures
………………………………………………………………………………………………
14
CHAPTER 3. ANALYSES ……………………………………………………………………………
16
Preliminary Analyses ……………………………………………………………………………….
16
Descriptive Statistics
…………………………………………………………………………..
16
Commitment Manipulation Check
………………………………………………………..
16
Confession Timing Manipulation Check ……………………………………………….
16
Attention Check …………………………………………………………………………………
17
Suspicion Check
…………………………………………………………………………………
17
Analytic Plan
…………………………………………………………………………………………..
17
Model 1: Total Effect of Confession Timing on Phase 2 Guilt Judgments …
18
Model 2: Belief Perseverance Effect …………………………………………………….
19
Path a: Confession Effect
…………………………………………………………………….
19
iv
Path b: Judgment Stability …………………………………………………………………..
20
Path a × b: Belief Perseverance ……………………………………………………………
20
Path c: Adding Confession Evidence and Procedural Effects …………………..
20
Moderation of Belief Perseverance by Commitment
……………………………….
22
Main Analyses ………………………………………………………………………………………..
22
Model 1: Total Effect of Confession Timing
………………………………………….
22
Model 2: Belief Perseverance Effect …………………………………………………….
23
Path a: Confession Effect
…………………………………………………………………….
24
Path b: Judgment Stability …………………………………………………………………..
24
Path a × b: Belief Perseverance ……………………………………………………………
25
Path c: Adding Confession Evidence and Procedural Effects …………………..
25
Path a × b + c: Total Effect of Confession Evidence
……………………………….
25
Moderation of Belief Perseverance by Commitment
……………………………….
26
CHAPTER 4. DISCUSSION
………………………………………………………………………….
27
Belief Perseverance
………………………………………………………………………………….
27
Commitment …………………………………………………………………………………………..
29
Accountability
…………………………………………………………………………………………
29
Limitations ……………………………………………………………………………………………..
30
Conclusion ……………………………………………………………………………………………..
31
REFERENCES …………………………………………………………………………………………….
33
APPENDIX A. PHASE 1 CRIME REPORT: CONFESSION EARLY ……………….
45
APPENDIX B. PHASE 1 CRIME REPORT: CONFESSION LATE ………………….
47
APPENDIX C. PHASE 2 CRIME REPORT ……………………………………………………
48
APPENDIX D. GUILT JUDGMENTS ……………………………………………………………
52
APPENDIX E. PERCEPTIONS OF IMPARTIALITY ……………………………………..
53
APPENDIX F. MANIPULATION CHECK …………………………………………………….
54
APPENDIX G. ATTENTION CHECK
……………………………………………………………
55
APPENDIX H. SUSPICION CHECK
……………………………………………………………..
56
APPENDIX I. SCRAMBLED ANAGRAMS …………………………………………………..
57
APPENDIX J. INSTITUTIONAL REVIEW BOARD APPROVAL FORM
………..
58
v
LIST OF FIGURES
Page
Figure 1. Participant Verdicts by Condition and Phase ………………………………………
37
Figure 2. Model 1: Examination of Total Effects ………………………………………………
38
Figure 3. Model 2: Mediated Model Examining Indirect Effects
…………………………
39
vi
LIST OF TABLES
Page
Table 1. Experimental Design
……………………………………………………………………….
40
Table 2. Descriptive Statistics
……………………………………………………………………….
41
Table 3. Correlations
……………………………………………………………………………………
42
Table 4. Correlations by Commitment Condition
…………………………………………….
43
Table 5. Model 2 Path Coefficients ……………………………………………………………….
44
vii
ACKNOWLEDGMENTS
I would like to thank some of the incredible mentors I have encountered leading up to this
thesis. To Dr. Leora Dahl for inspiring me to study forensic psychology rather than English. To
Dr. Linda Hatt and the late Dr. Claire Budgen for the opportunity to be a part of a research team
as an undergraduate. To Dr. Michael Woodworth for his mentorship of my honours thesis. To
Dr. Jan Cioe for his friendship and guidance on how to be a better student, a better teacher, and a
better person. To Dr. Marcus Credé and Dr. Gary Wells for their advice throughout the crafting
of this thesis. And finally to my co-advisors, Dr. Max Guyll and Dr. Stephanie Madon, for their
constant support and encouragement, without which this thesis would not have been possible.
viii
ABSTRACT
This research examined whether a criminal confession causes people to discount
subsequently encountered exculpatory evidence. Participants (N = 238) read a crime report
across two phases and judged a suspect’s guilt after each phase. In phase 1, the crime report
presented circumstantial evidence indicative of the suspect’s guilt. In phase 2, exculpatory
evidence indicative of the suspect’s innocence was added. The crime report manipulated whether
participants received confession evidence during phase 1 (confession–early) or phase 2
(confession–late). In addition, some participants publicly committed to their phase 1 guilt
judgments prior to receiving the crime report in phase 2 (high commitment), whereas others did
not (low commitment). Results provided some support for the hypothesis that a confession biases
the way that people use subsequently encountered exculpatory evidence to judge a suspect’s
guilt; under conditions of low commitment, participants more often rendered guilty verdicts in
the confession–early conditions than the confession–late conditions. The results are discussed in
terms of police investigator and juror decision-making.
1
CHAPTER 1. INTRODUCTION
It is well-established that a confession, even a false one, is a highly incriminating form of
evidence (Kassin, 2008; Leo & Drizin, 2010). Confession evidence is more powerful than
eyewitness and character testimony (Kassin & Neumann, 1997), and can even attenuate the
formidable power of DNA evidence under some conditions (Appleby & Kassin, 2016). Jurors
will sometimes convict defendants on the basis of confession evidence alone, and they do not
appropriately discount confessions that they believed were obtained under duress or that were
ruled inadmissible (Kassin et al., 2010; Kassin & Sukel, 1997; Smalarz, Madon, Yang, Guyll, &
Buck, 2016). Not surprisingly, jury conviction rates for false confessors are very high, ranging
from 73% – 81% (Drizin & Leo, 2004; Ofshe & Leo, 1997).
The power of confession evidence stems, in large part, from the widespread belief that
suspects, motivated by self-interest, would not confess to crimes that they did not commit unless
subjected to physical abuse or torture (Kassin & Wrightsman, 1981). However, psychological
research findings and proven false confession cases reveal this belief to be a misconception.
Innocent suspects do sometimes confess to crimes that they did not commit. In fact, false
confessions are a leading cause of wrongful convictions in the United States, contributing to the
convictions of nearly 28% of defendants who were later exonerated by DNA evidence (“DNA
Exonerations Nationwide,” 2016).
Although the widespread belief that false confessions only arise under egregious
circumstances is not true, it hints at the way that error and bias may contribute to the power of
confession evidence. That is, once people learn that a suspect has confessed, they may develop
such a strong belief in the suspect’s guilt that they fail to appropriately adjust their guilt
judgments in response to subsequently encountered evidence that points to the suspect’s
2
innocence. In psychological terms, a confession may elicit belief perseverance – a cognitive bias
in which people cling to their original beliefs even when the basis for the belief has been
discredited (Nestler, 2010). The idea that belief perseverance may contribute to the power of
confession evidence has been hypothesized by legal scholars (Findley & Scott, 2006), but has not
been empirically demonstrated.
Error and Bias
Social psychology has long emphasized the role that error and bias play in perception.
This emphasis dates back at least as far as the 1940s and 1950s when New Look in Perception
researchers proposed that people’s motivations, needs, goals, and expectations colored their
perceptions of reality (Bruner, 1992; Erdelyi, 1974). Bruner and Goodman (1947) provide a
classic illustration of this theoretical perspective. They presented 10-year-old children with coins
of varying values. In general, the children tended to overestimate the size of the coins, and this
tendency increased as the value of the coins increased. For example, children overestimated the
size of a penny by approximately 15%, whereas they overestimated the size of a quarter by more
than 35%. These results showed that the children’s perceptions of the coins were influenced by
their internal psychological states.
As a result of findings such as these, social and behavioral scientists turned their attention
to the way that biases may distort judgment and decision-making. Kahneman and Tversky
(1973), for instance, introduced numerous cognitive biases and heuristics, and in doing so called
into question the prevailing view that people rely on formal statistical rules to make social
inferences. For example, they argued that rather than using base rates to make judgments, people
instead have a tendency to make judgments on the basis of similarity, that people infer the
frequency of events according to the ease with which examples come to mind, and that people
3
are not sufficiently sensitive to the impact of sample size on probability judgments. The idea that
people rely on heuristics when making judgments sparked considerable interest in cognitive
biases and the way in which these biases may distort perception.
Belief Perseverance
Of particular importance to the current research is the cognitive bias of belief
perseverance. As previously noted, belief perseverance is the tendency for people to cling to their
initial beliefs even after the foundation supporting those beliefs has been discredited (Nestler,
2010). Numerous studies in the basic psychological literature have demonstrated this effect, with
most relying on what is commonly referred to as the debriefing paradigm.
The debriefing paradigm involves two groups of participants who receive conflicting
information about a topic. Participants in both groups subsequently learn that the information
they received is false, after which they make judgments relevant to the discredited information.
Although logically, participants should not use the discredited information to make their
judgments, the literature consistently shows that they do. For example, following a
discrimination task, participants who received positive feedback rated themselves as having
greater discrimination abilities than participants who received negative feedback despite that all
participants had earlier been informed that the feedback was false (Ross, Lepper, & Hubbard,
1975). Similarly, participants who were initially informed of a positive relationship between risk-
taking and being a successful firefighter continued to rate risky behavior as diagnostic of
firefighting success despite having already been debriefed to the false nature of the relationship
(Anderson, Lepper, & Ross, 1980).
A key strength of the debriefing paradigm is that it permits a decisive test of the belief
perseverance effect. That is, because the information on which participants based their initial
4
beliefs was completely discredited, any subsequent between-group difference in judgments that
is in the direction of the discredited information shows that participants inappropriately used the
discredited information. However, it is important not to equate the paradigm with the effect.
Even though the debriefing paradigm involves the complete discrediting of information, the
concept of belief perseverance does not. Failure to revise a belief when the information on which
it was based has been partially discredited is also irrational and also constitutes belief
perseverance. In addition, restricting the concept of belief perseverance only to situations
involving the complete discrediting of information raises conceptual problems. Most notably, it
would mean that beliefs that persevered in the context of less than completely discredited
information could not, by definition, indicate belief perseverance. This would be the case even if
the degree of discrediting was as high as 99%, and even though the underlying psychological
process responsible for the effect is indistinguishable from the process that operates when the
degree of discrediting is complete.
In fact, psychological theory never conceptualized belief perseverance as restricted to
situations involving the complete discrediting of information. For example, in the opening
paragraphs of Ross et al.’s (1975) seminal article on the belief perseverance effect, the authors
provided examples that specifically involved the partial discrediting of information: a teacher
attributes a student’s disengagement to lack of motivation, but later learns that the student is
undernourished and sleep deprived; a woman infers romantic interest from a man who gives her
flowers, but later learns that the man’s father is a florist. In both of these examples, the new
information partially discredited the foundation upon which the original beliefs were based by
way of offering alternative explanations. The logical response would be for the teacher and the
5
woman to revise their beliefs in a manner commensurate with the degree of discrediting. A
failure to do so would indicate belief perseverance.
Although Ross et al. (1975) recognized that belief perseverance can occur in the context
of partially discredited information, their experiments used the debriefing paradigm as a way to
avoid the complexities created by partially discredited information. However, subsequent to the
publication of their article, a number of studies have examined belief perseverance in the context
of partially discredited information. These studies, which investigated the belief perseverance
effect with a wide-range of topics (e.g., capital punishment, judgments of a suspect’s guilt,
attitudes toward Richard Nixon) underscore the point that belief perseverance occurs under a
broader set of conditions than the debriefing paradigm permits (Carretta & Moreland, 1982;
Marksteiner, Ask, Reinhard, & Granhag 2011; Lord, Ross, & Lepper, 1979).
The Power of Confession Evidence
People’s tendency to show belief perseverance may help to explain the power of
confession evidence. Once a suspect has confessed, people tend to develop an initial expectation
or presumption of guilt (Kassin & Neumann, 1997). Moreover, because of the widespread belief
that innocent suspects would not confess to crimes that they did not commit, it stands to reason
that people would likely hold this initial presumption of guilt quite strongly (Kassin &
Wrightsman, 1981). This is not to say that people necessarily presume innocence in the absence
of a confession, but rather that a confession increases the certainty or strength with which people
presume guilt. Further, even though it is not irrational for a confession to have this effect (a
confession should produce a stronger presumption of guilt than if no confession was present) it
can still have negative consequences for suspects’ outcomes.
6
For example, a confession that is obtained early in a police investigation may cause
detectives to discount subsequently discovered exculpatory evidence more than they would have
had the confession been obtained at the same time or after the exculpatory evidence. High
profile, proven false confession cases illustrate this hypothesized effect. The police and
prosecutor in Jeffrey Deskovic’s case continued to believe in the validity of his confession even
after learning that DNA recovered from the victim excluded him (Leo & Drizin, 2010).
Similarly, the police and prosecutor in the case of the Central Park Five continued to believe in
the validity of the confessions made by the five teenagers accused of the brutal attack and rape of
a jogger in New York City’s Central Park even after discovering that their confessions were
riddled with inconsistencies, did not correspond to witness statements, and that DNA recovered
from the victim did not implicate them (Weiss, Watson, & Cynwyd, 2013).
Although proven false confession cases such as these provide anecdotal evidence that a
confession can lead people to cling to the belief that a suspect is guilty despite the subsequent
discovery of exculpatory evidence, only one study has empirically tested this effect (More,
Madon, Guyll, & Atkinson, 2015). Participants in the study read a crime report across two
phases, rating the suspect’s guilt at each phase. In phase 1, the crime report described
circumstantial evidence that pointed toward the suspect’s guilt. In phase 2, exculpatory evidence
that pointed toward the suspect’s innocence was added. All participants also received confession
evidence, but half of the participants receive it during phase 1, whereas the other half received it
during phase 2. Therefore, all participants ultimately received identical evidence, with the only
variation being when the confession evidence was presented.
The authors hypothesized that participants who received confession evidence before the
exculpatory evidence would be more likely than participants who received it alongside the
7
exculpatory evidence to presume that the suspect was guilty. However, the findings did not
support this hypothesis. Instead, the findings indicated that the timing of the confession evidence
did not influence participants’ judgments of the suspect’s guilt at phase 2. Consideration of the
study’s methods suggests two factors that may have contributed to this non-significant effect.
Ambiguity
One aspect of the study that may have contributed to the non-significant effect was the
nature of the exculpatory evidence. Because More et al. (2015) relied on clearly unambiguous
exculpatory evidence, participants may have had no reason to doubt the suspect’s innocence. A
large literature in psychology indicates that ambiguity increases people’s susceptibility to
cognitive biases (Tversky & Kahneman, 1974). In fact, this is a central thesis of the literature on
error and bias – i.e., that people use heuristics when making probabilistic judgments. Therefore,
it is possible that participants in More et al.’s study might have been more likely to discount the
exculpatory evidence in favor of their initial guilt judgments had it been ambiguous rather than
clearly unambiguous. According to this reasoning, the hypothesized belief perseverance effect
may be more likely when a confession is discredited by ambiguous, rather than clearly
unambiguous, exculpatory evidence.
Commitment
A second aspect of More et al.’s (2015) procedures that may have contributed to the non-
significant belief perseverance effect is that participants were not particularly motivated to
maintain their initial guilt judgments. This possibility is consistent with a core theme that runs
throughout the psychological literature; namely, that motivational factors influence people’s
beliefs and behaviors. For example, Cialdini (1984) outlined six key principles of social
influence, one of which was the principle of commitment and consistency. According to this
8
principle, a central motive that influences people’s behavior is the need to behave consistently
with their previously established beliefs (Cialdini, 1999). If people commit to a belief or
behavior, then they are more likely to maintain that belief or behavior at a later point in time
(Cialdini, 1984), an effect that has received strong empirical support (Baca-Motes, Brown,
Gneezy, Keenan, & Nelson, 2013; Dickerson, Thibodeau, Aronson, & Miller, 1992).
The principle of commitment and consistency may also be relevant to understanding how
belief perseverance operates in the context of criminal investigations. Due to internal and
external pressures to capture perpetrators and solve crimes, police investigators may be
motivated to maintain their beliefs in a suspect’s guilt after obtaining a confession. Put
differently, after police investigators have obtained a confession from a suspect, they may be
disinclined to revise their judgments about the suspect’s guilt even if they later discover
exculpatory evidence. Therefore, the hypothesized belief perseverance effect may partly depend
on people’s motivation to maintain their initial beliefs, with stronger effects occurring under
conditions of high commitment.
Research Overview and Hypotheses
This research tested two hypotheses. First, it tested the hypothesis that people who
encounter confession evidence before encountering exculpatory evidence are more vulnerable to
belief perseverance than people who encounter confession and exculpatory evidence
simultaneously. Second, it tested whether this predicted effect is moderated by people’s
commitment to their initial beliefs about a suspect’s guilt, with stronger effects occurring among
people who are highly committed. The research tested these hypotheses in the context of an
experiment that manipulated whether participants encountered confession evidence before or at
9
the same time as exculpatory evidence, and whether or not they publicly committed to an initial
judgment of a suspect’s guilt prior to receiving exculpatory evidence.
10
CHAPTER 2. METHOD
Power Analysis
The statistical software G*Power was employed to estimate the appropriate sample size
necessary to detect main effects of confession timing and commitment, plus an interaction effect
involving these variables (Faul, Erdfelder, Lang, & Buchner, 2007). The analysis was conducted
using the conventional power value of 1-b = 0.80 at an alpha level of α = .05 (Cohen, 1992). The
only known previous study examining confession evidence and belief perseverance had non-
significant results with a moderate effect size, Cohen’s f = .21 (More et al., 2015). Moreover,
studies such as Dickerson et al. (1992) have found a moderate effect of commitment on behavior,
Cohen’s f = .27. With these studies in mind, a moderate effect size, Cohen’s f = .25, was used to
estimate the sample size (Cohen, 1988). Using this estimate, the power analysis indicated that a
sample size of 179 would be required to achieve the desired level of power. The sample size of
the current research exceeded this minimum.
Participants
Participants (N = 250) were Iowa State University students who participated in exchange
for partial fulfillment of a course requirement. Eight participants were excluded for failing two
key attention check questions, and four experimental sessions were terminated due to a computer
malfunction. Therefore, there were 238 participants in the final sample, including 84 men and
154 women between the ages of 18 and 50 with a mean age of 19.46 years. There were 199
European Americans, 10 Asian Americans, 9 Latin Americans, 8 African Americans, 1 Native
American, and 11 participants who identified as multi-ethnic. All participants were native
English speakers. This study was approved by the Institutional Review Board at Iowa State
University (Appendix J).
11
Design
Participants were randomly assigned to a 2 (phase: phase 1 vs. phase 2) × 2 (confession
timing: early vs. late) × 2 (commitment: high vs. low) mixed-model experimental design, with
repeated measures on the factor of phase (see Table 1). Confession timing manipulated whether
participants received confession evidence before (phase 1) or at the same time as (phase 2)
exculpatory evidence. Participants in the confession–early conditions received the confession
evidence before the exculpatory evidence (phase 1), whereas participants in the confession–late
conditions received the confession and exculpatory evidence simultaneously (phase 2).
Commitment manipulated the degree to which participants were motivated to maintain their
phase 1 judgment of a suspect’s guilt. Participants in the high commitment conditions publicly
revealed their phase 1 guilt judgments to the experimenter and signed a form confirming their
judgment immediately after phase 1 and prior to beginning phase 2. Participants in the low
commitment conditions neither publicly revealed nor confirmed their phase 1 guilt judgments
prior to beginning phase 2.
Crime Report
A fictional crime report (see Appendices A, B, and C) described an assault and theft in
which a male assailant struck a woman on the head from behind and stole her purse as she was
entering a car in a parking lot. The victim was unable to describe the perpetrator, and footage
from a surveillance video was too grainy to be useful. Based on the circumstantial evidence,
Kyle James became the prime suspect. During an interrogation, James confessed to the crime,
but later recanted his confession, claiming that he had been at a local restaurant when the crime
occurred. His alibi was supported by a credit card transaction and a questionable eyewitness
identification.
12
Measures
Guilt Judgments
Participants judged the suspect’s guilt by responding to three questions: (1) “Based on the
information presented in the criminal report, if you had to choose, would you say that Kyle
James is more likely to be guilty or innocent?”, with response options 1 (guilty) and 2 (innocent),
(2) “How confident are you in your decision?”, with endpoints 1 (not at all confident) and 10
(very confident), and, (3) “How likely do you think it is that James is guilty?”, with endpoints 1
(very unlikely) and 10 (very likely). Participants responded to these questions twice, once during
phase 1 and then again during phase 2 (see Appendix D). These variables are subsequently
referred to as verdict, confidence, and likelihood of guilt.
Perceptions of Impartiality
Two questions assessed the degree to which participants perceived themselves as having
provided an impartial judgment of the defendant’s guilt: (1) “To what extent was your evaluation
based on the evidence provided within the crime report?”, with endpoints 1 (not at all evidence-
based) and 10 (completely evidence-based); and (2) “How impartial was your evaluation of the
case?”, with endpoints 1 (not at all fair and impartial) and 10 (very fair and impartial).
Participants’ responses to these questions were averaged to create one score per participant with
higher scores corresponding to greater levels of perceived impartiality. Participants answered
these questions during phase 2 (see Appendix E).
Manipulation Check
Participants answered five manipulation check questions (see Appendix F). One question
used a multiple-choice format to assess whether participants correctly recalled the confession.
Responses were coded as 1 (correct) and 0 (incorrect). The four remaining manipulation check
13
questions assessed the strength of participants’ commitment to their guilt judgments: (1) “After
you read the crime report for the first time, how strong was your belief that the suspect was
guilty or innocent?”, with endpoints 1 (very weak belief) and 10 (very strong belief), (2) “After
you read the crime report for the first time, how strong would new evidence had to have been for
you to change your verdict from guilty to innocent or innocent to guilt?”, with endpoints 1 (not
very strong) and 10 (very strong), (3) “Thinking about your final verdict in this case, how
difficult would it be for someone to convince you to change your verdict from guilty to innocent
or from innocent to guilty?”, with endpoints 1 (not very difficult) and 10 (very difficult), and (4)
“Thinking about your final verdict in this case, how strong would new evidence have to be for
you to change your verdict from guilty to innocent or innocent to guilty?”, with endpoints 1 (not
very strong) and 10 (very strong). Participants’ responses to these four questions were averaged
to create one score per participant with higher scores indicating greater commitment to their guilt
judgments.
Attention Check
Eight questions assessed the extent to which participants attended to the crime report (see
Appendix G). These questions asked participants to recall the suspect’s name, whether the
suspect confessed to the crime, what the suspect’s alibi was, and the circumstantial evidence that
the police had against the suspect. Responses were coded as 1 (correct) and 0 (incorrect) and
summed to create one score per participant that ranged from 0 to 8, with higher scores indicating
a greater degree of attentiveness to the crime report.
Suspicion Check
Four questions assessed participants’ general level of suspicion, prior knowledge about
the experiment, and the degree to which they perceived the experimenter to be credible (see
14
Appendix H): (1) “Sometimes experiments study questions that are not obvious. Do you believe
that is the case in this experiment?”, with response options 1 (yes) and 2 (no), (2) “If yes, please
indicate what research question(s) might be under investigation in this experiment.” (open-
ended), (3) “Please indicate what you knew about this experiment before participating.” (open-
ended), and (4) “Please rate as honestly as possible how believable you found the experimenter
when he or she informed you that some of the materials had been left out. This question will
remain anonymous and the experimenter will never learn of your rating.”, with endpoints 1
(completely unbelievable) and 6 (completely believable). Responses were evaluated to identify
participants who identified the research hypotheses, had prior knowledge of the experimenter, or
were suspicious about the feigned experimental mistake.
Scrambled Anagrams
As a filler task, all participants attempted to solve up to 44 scrambled anagrams within
four minutes (see Appendix I). Pilot testing showed that college students can complete an
average of 20 anagrams in this timeframe, with a minimum and maximum of 9 and 32,
respectively. The filler task was included to provide a window of time that supported a feigned
claim by the experimenter that a portion of the crime report had accidentally been omitted from
the materials, thus necessitating that they receive the full crime report and respond to the
questions a second time. Because the scrambled anagram task is unrelated to the hypotheses
under investigation, it was not scored or used in any of the analyses.
Procedures
Participants were run individually. Upon arrival to the experimental session, the
participant signed a consent form and was told that the study was designed to examine how
people evaluate evidence in a criminal case. The experimenter then explained that the participant
15
would review evidence from a real, ongoing case after which the participant received a portion of
a crime report that included circumstantial evidence (phase 1). This portion of the crime report
also included confession evidence for participants in the confession–early conditions. After
reading this portion of the crime report, the participant made several guilt-relevant judgments
including a verdict (guilty vs. innocent), confidence rating, and likelihood of guilt judgment. The
commitment manipulation occurred immediately after.
In the high commitment conditions, the participant publicly stated his or her phase 1
verdict (guilty vs. innocent) and signed a form confirming it. Participants performed these tasks
believing that the signed form would be sent to the county prosecutor’s office to help with the
case. To support the veracity of this claim, the experimenter placed the participant’s signed form
in an envelope addressed to the county prosecutor’s office and left the room under the guise of
depositing it in the mail. In the low commitment conditions, the participant did not publicly state
his or her phase 1 verdict, nor sign any form to confirm it.
Following the commitment manipulation, the participant was left alone to work on the
filler task for four minutes. Afterward, the experimenter informed the participant that during the
filler task, she or he had discovered that a portion of the crime report had accidentally been
omitted, thus necessitating that the participant read the full crime report and answer the questions
a second time. After having done so, the participant responded to the manipulation checks,
attention checks, suspicion checks, and reported demographic information. After all measures
had been completed, the experimenter fully debriefed the participant.
16
CHAPTER 3. ANALYSES
Preliminary Analyses
Descriptive Statistics
Table 2 presents the means, standard errors, and confidence intervals for participants’
verdicts, confidence ratings, and likelihood of guilt judgments organized by experimental
condition. Table 3 presents the correlations between variables for the entire sample whereas
Table 4 presents the correlations separately for participants in the low commitment and high
commitment conditions. Figure 1 presents participants’ verdicts, which are shown by condition
and phase as they proceeded through the study.
Commitment Manipulation Check
An independent samples t-test assessed the effectiveness of the commitment
manipulation. Results indicated no significant difference in self-reported commitment levels
between participants in the low commitment and high commitment conditions, t (236) = 0.80, p
= .427, d = .10. Note that d values of .2, .5, and .8 correspond to small, medium, and large
effects, respectively (Cohen, 1988). These results suggest either that the commitment
manipulation was unsuccessful or that the self-report questionnaire failed to properly assess
participants’ commitment levels.
Confession Timing Manipulation Check
A frequency analysis indicated that 210 participants (88.2%) correctly identified whether
the confession was presented during phase 1 or phase 2, whereas 28 (11.8%) incorrectly reported
its timing. A series of independent samples t-tests that compared participants who correctly and
incorrectly answered the confession timing manipulation check question revealed no significant
differences in their phase 2 likelihood of guilt judgments, t (236) = -0.55, p = .586, d = .11, or
