The Truth About the Truth: A Meta-Analytic Review of the Truth Effect

Abstract

Repetition has been shown to increase subjective truth ratings of trivia statements. This truth effect can be measured in two ways: (a) as the increase in subjective truth from the first to the second encounter (within-items criterion) and (b) as the difference in truth ratings between repeated and other new statements (between-items criterion). Qualitative differences are assumed between the processes underlying both criteria. A meta-analysis of the truth effect was conducted that compared the two criteria. In all, 51 studies of the repetition-induced truth effect were included in the analysis. Results indicate that the between-items effect is larger than the within-items effect. Moderator analyses reveal that several moderators affect both effects differentially. This lends support to the notion that different psychological comparison processes may underlie the two effects. The results are discussed within the processing fluency account of the truth effect.

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DOI: 10.1177/1088868309352251
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Alice Dechêne, Christoph Stahl, Jochim Hansen and Michaela Wänke
The Truth About the Truth: A Meta-Analytic Review of the Truth Effect
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The Truth About the Truth: A Meta-Analytic
Review of the Truth Effect
Alice Dechêne1, Christoph Stahl2, Jochim Hansen1,
and Michaela Wänke1
Abstract
Repetition has been shown to increase subjective truth ratings of trivia statements. This truth effect can be measured in
two ways: (a) as the increase in subjective truth from the first to the second encounter (within-items criterion) and (b) as the
difference in truth ratings between repeated and other new statements (between-items criterion). Qualitative differences are
assumed between the processes underlying both criteria. A meta-analysis of the truth effect was conducted that compared
the two criteria. In all, 51 studies of the repetition-induced truth effect were included in the analysis. Results indicate that the
between-items effect is larger than the within-items effect. Moderator analyses reveal that several moderators affect both
effects differentially. This lends support to the notion that different psychological comparison processes may underlie the two
effects. The results are discussed within the processing fluency account of the truth effect.
Keywords
truth effect, meta-analysis, processing fluency
When presented with an unfamiliar statement, such as “The
zipper was invented in Norway,” most people do not know
whether it is actually true or not (i.e., the statement is ambig-
uous).1 To nevertheless judge a statement’s truth, people tend
to use heuristic cues. Such heuristics make use of attributes
of the statement’s source (e.g., the source’s level of expertise
on the subject matter), attributes of the context in which it is
presented (e.g., at a scientific conference), and attributes of
the statement itself. In particular, it has been shown that
people tend to trust a statement more if it had been encoun-
tered before: After reading “The zipper was invented in
Norway” for a second time, judgments of the statement’s
truth or validity typically increase. This so-called truth effect
has been the subject of extended study in psychological (e.g.,
Arkes, Boehm, & Xu, 1991; Bacon, 1979; Begg, Anas, &
Farinacci, 1992; Hasher, Goldstein, & Toppino, 1977) and
consumer research (e.g., Hawkins & Hoch, 1992; Law,
Hawkins, & Craik, 1998; Roggeveen & Johar, 2002, 2007).
It is important to understand this effect because people’s
trust in statements’ truth may affect behavior related to those
statements (e.g., marketing claims, health beliefs).
The present article presents a meta-analytic review of
research on the truth effect that aims at integrating past research
and providing a common basis for systematic future research.
In addition, it seeks to open new avenues for research. It
attempts to do so by focusing on two theoretically important
factors that have rarely been investigated so far, namely, the
distinction between two components of the truth effect (i.e.,
the within-items component and the between-items compo-
nent) and the context in which statements are judged. The
theoretical analysis in this review is based on the current con-
sensus that the truth effect is mediated by the metacognitive
experience of processing fluency (Begg et al., 1992; Reber
& Schwarz, 1999; Unkelbach, 2007; Whittlesea, 1993; for a
review, see Alter & Oppenheimer, 2009). In short, process-
ing a repeated statement is experienced as unexpectedly
fluent—in other words, the processing fluency is experienced
as discrepant from a comparison standard—and this dis-
crepancy subsequently affects judgments of truth (e.g., Hansen,
Dechêne, & Wänke, 2008; Whittlesea & Williams, 1998,
2000, 2001a, 2001b). Here we focus on the prediction that the
comparison standard—and, thereby, the truth effect—should
vary with the context in which judgments are made (e.g.,
Dechêne, Stahl, Hansen, & Wänke, 2009; Whittlesea &
Leboe, 2003).
We distinguish between two types of judgment contexts
that differ with regard to the variability of the stimuli with
which participants are confronted: First, truth judgments can be
1University of Basel, Basel, Switzerland
2University of Freiburg, Freiburg, Germany
Corresponding Author:
Alice Dechêne, University of Basel, Department of Psychology,
Missionsstrasse 60/62, CH-4055 Basel, Switzerland
Email: alice.dechene@unibas.ch
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Dechêne et al. 239
collected in a homogeneous context in which a homogeneous
set of repeated items is judged. To assess the effect of repeti-
tion, these judgments are compared to those collected for the
same set of statements at their first encounter; we call this the
within-items criterion. Second, truth judgments can be col-
lected in a heterogeneous context in which a mixture of
repeated and nonrepeated statements is judged. To assess the
effect of repetition, judgments of a set of repeated statements
are compared to judgments of a different set of nonrepeated
statements; we call this the between-items criterion. To shed
light on contextual influences on the truth effect, the meta-
analysis separately evaluates the between- and within-items
criteria, both with regard to the magnitude of the effect and
with regard to influences of potential moderating variables
discussed in the literature.
In the remainder of this introduction, the literature on the
truth effect is briefly reviewed. The discussion of mediating
variables focuses on processing fluency and the important
role of the comparison standard. The distinction between
contexts is elaborated, and hypotheses for a comparison of
the two criteria are derived. Before turning to the meta-analysis,
potential moderating variables are addressed and the focus of
the present review is summarized.
The Truth Effect
In a typical study on the truth effect, a set of ambiguous state-
ments (i.e., statements whose truth status is unknown to
participants, as established by pretests) is presented to par-
ticipants in a first session. In a second session, some of the
statements are presented and judged again, often interspersed
with new statements that have not been presented before.
Repeated presentation of an ambiguous statement increases
the probability that it will be judged as true (e.g., Bacon, 1979;
Hasher et al., 1977; Schwartz, 1982). This effect belongs to
a family of well-known effects of repetition in psychology,
such as the mere exposure effect (Bornstein, 1989; Zajonc,
1968) and the false-fame effect (Jacoby, Kelley, Brown, &
Jasechko, 1989).
The finding that repeated statements are believed more
than new ones (e.g., Hasher et al., 1977) has been obtained
under many conditions. The effect has been demonstrated
for trivia statements (Bacon, 1979), product-related claims
(Hawkins & Hoch, 1992; Law et al., 1998; Roggeveen &
Johar, 2002, 2007), and even opinion statements (Arkes,
Hackett, & Boehm, 1989). It occurs for orally presented
statements (Gigerenzer, 1984; Hasher et al., 1977) and writ-
ten statements (e.g., Arkes et al., 1989; Schwartz, 1982) as
well as with a delay of minutes (Arkes et al., 1989; Begg &
Armour, 1991; Begg, Armour, & Kerr, 1985; Begg et al.,
1992; Schwartz, 1982) or weeks (Bacon, 1979; Gigerenzer,
1984; Hasher et al., 1977) between the repetitions of the
statements. The effect has been shown with different presen-
tation times of each statement (5 s to 12 s; Gigerenzer, 1984),
and it occurs when the truth of each statement is rated after
each repetition (Hasher et al., 1977) or when the rating takes
place only after the final repetition (Schwartz, 1982). The
effect generalizes to nonlaboratory settings (Gigerenzer,
1984), it has been shown that one exposure to a statement is
sufficient to produce the effect (Arkes et al., 1991), and it
seems to be robust against feedback after a longer delay
(Brown & Nix, 1996; Skurnik, Yoon, Park, & Schwarz,
2005). It occurs equally for actually true and actually false
statements (Brown & Nix, 1996). Moreover, even repeated
statements from a noncredible source are judged as more
probably true as compared to new statements (Begg et al.,
1992). Overall, the truth effect appears to be very robust. The
only constraint seems to be that the statements have to be
ambiguous, that is, participants have to be uncertain about
their truth status because otherwise the statements’ truthful-
ness will be judged on the basis of their knowledge and not
on the basis of fluency.
Mediating Variables: The Role of Memory Processes. By
definition, the repetition-based truth effect is mediated by
memory processes. Different memory processes have been
discussed, for example, memory for stimulus frequency
(Hasher et al., 1977), explicit recognition (Bacon, 1979;
Hawkins & Hoch, 1992), familiarity (Begg et al., 1992;
Schwartz, 1982), and, more recently, processing fluency (e.g.,
Begg et al., 1992; Reber & Schwarz, 1999; Unkelbach, 2006,
2007). Although these suggested mediators are all based on
memory, they differ with regard to important qualities. A
first important distinction is that between source memory
and item memory: On one hand, if we remember hearing a
statement from a particular source (e.g., from a distinguished
expert), this information provides referential validity and likely
increases our judgment of the statement’s truth—given the
source is trustful (e.g., Brown & Nix, 1996). The role of ref-
erential validity is limited in most studies because statements
are usually pretested to be unfamiliar to participants. On the
other hand, just remembering having heard the statement
itself before (i.e., without source information) can increase
truth judgments, too (Arkes et al., 1991): Remembering pre-
vious occurrences of a statement conveys what can be called
convergent validity.2
The second important distinction is that between explicit
and implicit memory processes: Although explicit recogni-
tion of a statement is clearly necessary for referential or
convergent validity effects to occur, a nonreferential truth
effect can consistently be observed even in the absence of
explicit recollection (Bacon, 1979); it is this nonreferential,
implicit part of the truth effect that is thought to be driven by
processing fluency (Begg et al., 1992; Reber & Schwarz,
1999; Unkelbach, 2007). Importantly, although source and
even item memory provide a rational basis for the truth
effect, this is not the case for the fluency-based part of
the effect, which is why it has been termed the illusory truth
effect (Begg et al., 1992).
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240 Personality and Social Psychology Review 14(2)
Processing Fluency and the Truth Effect. Processing fluency
is defined as the metacognitive experience of ease during
information processing; it may be elicited, for example, by
linguistic ease, perceptual ease, semantic priming, or retrieval
ease (Alter & Oppenheimer, 2009; Whittlesea, 1993). For
instance, processing fluency can be increased by improv-
ing the visual contrast with which a stimulus is presented on
a computer screen: A higher contrast makes it easier for
participants to perceive the stimulus. This perceptual ease—
or, more generally, processing fluency—may subsequently
affect judgments; for example, it may lead individuals to rate
statements more probably true when presented in high as
compared to low visual contrast (Reber & Schwarz, 1999).
In addition to truth judgments, the fluency experience has
been shown to affect a broad variety of domains (cf. Alter &
Oppenheimer, 2009), including confidence (e.g., Simmons &
Nelson, 2006), familiarity judgments (e.g., Whittlesea, 1993),
and attractiveness (Reber, Winkielman, & Schwarz, 1998).
Taken together, repetition affects judgments of a statement’s
truth value by increasing processing fluency: A statement that
is processed more fluently is typically more likely to be judged
true (e.g., Begg et al., 1992).3
For fluency to inform judgments, one has to form an idea
of how fluent a given experience was; this implies that a com-
parison must be made with a norm or standard (Whittlesea &
Leboe, 2003). Depending on the standard, a given experi-
ence is then interpreted as relatively fluent (i.e., if it exceeds
the standard) or as relatively disfluent (i.e., if it falls below
the standard). In other words, for processing fluency to affect
judgments, it needs to be experienced as discrepant from a
comparison standard (Hansen & Wänke, 2008; Westerman,
2008; Whittlesea & Williams, 1998, 2000, 2001a, 2001b;
Willems & Van der Linden, 2006). The experience of discrep-
ancy has been shown to play an important role in effects of
repetition on truth judgments (Dechêne et al., 2009; Hansen
et al., 2008). Despite its theoretical importance, not much is
known about how comparison standards are chosen or about
the variables that affect this choice. What we do know is that
the comparison standard appears to depend on features of the
stimuli and of the context in which stimuli are encountered
(e.g., Whittlesea & Leboe, 2003). Recent findings suggest
that a standard may be based, for instance, on an expectation
held in mind about how easily a stimulus will be processed
(Hansen et al., 2008; Hansen & Wänke, 2008; Whittlesea
& Leboe, 2003; Whittlesea & Williams, 1998, 2000, 2001a,
2001b) or on the average processing fluency of other stim-
uli in the same context (Dechêne et al., 2009; Whittlesea &
Leboe, 2003).
At this point, the mediation of the repetition-based truth
effect by processing fluency can be summarized as follows:
In a first step, fluency is enhanced by repeated processing;
in a second step, the enhanced processing fluency is experi-
enced as discrepant from a comparison standard; in a third
step, the experienced discrepancy informs truth judgments.
Contextual Influences on the Comparison Standard. In the
present review, we argue that the truth effect may be affected
by the judgment context via its influence on the construction of
a comparison standard. We distinguish between two different
contexts in which the critical truth judgments are collected: a
homogeneous and a heterogeneous context. Below, it is out-
lined how these contexts may differentially affect the
comparison standard and, thereby, the truth effect.
The heterogeneous context. Here, truth judgments are col-
lected for a heterogeneous mix of statements, consisting of a
set of repeated and a different set of nonrepeated statements.
The truth effect is assessed using the between-items criterion:
Truth judgments for the critical set of repeated statements
are compared to those for a different set of statements that
were not encountered before. In the heterogeneous context,
because of the mixture of repeated and nonrepeated state-
ments, there is considerable variability in processing fluency.
This variability has at least two consequences: First, partici-
pants may notice that some statements are more fluent than
others, and they may be more likely to use this information
as a heuristic cue to inform their judgments. Second, and
most importantly, the heterogeneous context provides a situ-
ation in which a useful and precise comparison standard can
be easily construed on the fly based on the statements’ aver-
age fluency (Whittlesea & Leboe, 2003). With the average
fluency as a comparison standard, repeated statements are
likely to be perceived as above average whereas nonrepeated
statements are perceived as below average. Such an average
standard is the most efficient way to classify items as fluent
versus disfluent, as repeated versus new, or as more versus
less likely true. In addition, the contrast in fluency between
fluent and disfluent stimuli may lead to a shift of judgments
of nonrepeated items toward the “false” end of the scale. We
call this the negative truth effect. If such an effect were to
exist, it would inflate the between-items criterion but would
not affect the within-items criterion (i.e., because the latter
does not consider judgments of nonrepeated statements).
The homogeneous context. In the homogeneous context,
truth judgments are collected for a homogeneous set of
repeated statements only. The truth effect is assessed using
the within-items criterion: Truth judgments are compared to
those made to the same set of statements at the first encoun-
ter. In contrast to the heterogeneous context, there is little
variability in processing fluency in the homogeneous context.
As a consequence, processing fluency conveys no informa-
tion and is less likely to be recruited as a cue by participants
(Whittlesea & Leboe, 2003).
Furthermore, if fluency is nevertheless used, a sensible
comparison standard is not easily construed. Using average
fluency as a standard is obviously not useful here; it would
render all statements equally nondiscrepant from the stan-
dard. Global standards or expectancies form other possible
bases for a comparison standard (e.g., Hansen et al., 2008;
Whittlesea & Leboe, 2003): A global expectancy may be
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Dechêne et al. 241
formed on the basis of previous experience but will likely
lead to a rather diffuse comparison standard. Perhaps the
most useful expectancy to be recruited is based on the spe-
cific statements’ processing fluency at previous encounters;
it might lead to a less diffuse standard but depends on partici-
pants’ ability to retrieve their processing fluency experiences
from the first session. It is unclear whether and how fluency
experiences are stored in memory; given that fluency is a
rather subtle perceptual signal, memory for this signal is
likely to decline substantially as a function of intersession
delay. Other standards may also be used, but such standards
are likely to be idiosyncratic and more variable across par-
ticipants as they are less restrained by the context. Because
the homogeneous context provides no information about the
relevant range of processing fluency, the comparison stan-
dards are likely to be more variable on two levels: Within
participants, they may rely on more diffuse prior expectan-
cies; furthermore, expectancies are more likely to differ
between participants. As a result, the use of fluency is ren-
dered both less likely and less efficient.
Thus, although the truth effect is driven by fluency discrep-
ancy in both contexts, the comparison standards may differ
across contexts: In the absence of relevant contextual infor-
mation in the homogeneous context, the truth effect in this
context may, for example, be based on an individual’s rather
diffuse global fluency expectancies. In contrast, in the hetero-
geneous context, the truth effect is likely to be based on a
more specific standard computed on the fly from the informa-
tion provided by that context. From these differences, three
predictions can be derived that will be the focus of the meta-
analysis. First, the truth effects in the two contexts should
differ in magnitude (i.e., the effect should be larger in the het-
erogeneous than in the homogeneous context); second, they
might be affected differently by moderating variables (e.g.,
by moderators that affect the construction of the comparison
standard). A third prediction is that a negative truth effect
should be observed in the heterogeneous context: Nonre-
peated statements should be less likely to be judged true when
judged in the context of repeated statements as compared to
when judged in the context of other nonrepeated statements.
These predictions are evaluated in the meta-analysis by com-
paring the between-items and within-items criteria.
Note that the postulated links between the within-item
criterion and the homogeneous context, and between the
between-item criterion and the heterogeneous context, are not
perfect: Although a truth effect in a homogeneous context is
necessarily measured using the within-items criterion, a truth
effect obtained in a heterogeneous context can often be mea-
sured using either criterion. Specifically, the within-items
criterion can also be computed for the heterogeneous context
(provided that first-session truth ratings are available). In
fact, a large proportion of the within-items effect sizes in the
meta-analysis are from heterogeneous contexts. This implies
that the meta-analytic results obtained for the within-items
effect were also, to a substantial extent, driven by the het-
erogeneous context. Hence, for separating the effects of the
different contexts, the present comparison between the two
criteria must be seen as a rough initial assessment that should
be followed and complemented by more targeted experimen-
tal research (e.g., Dechêne et al., 2009).
Moderating Variables
A variety of moderators of the truth effect have been investi-
gated. First, as mentioned above, the truth effect is observed
only for ambiguous statements; it disappears when the actual
truth status is known. Evidence for this comes from findings
that the truth effect disappears when feedback about the
actual truth status is given (Brown & Nix, 1996). However,
when a delay is introduced between feedback and judgment,
causing memory for the actual truth status to decline, the
effect reappears.
Several attributes of the statements’ source also moderate
the truth effect. Overall, repeated statements from credible
sources are believed more, as compared to repeated state-
ments from noncredible sources (when source credibility is
remembered). However, repeated statements from non-
credible sources are still believed more, as compared to new
statements from those sources (Begg et al., 1992). This result
indicates that source credibility moderates the size of the
effect, but it does not completely eradicate the truth effect. In
addition, statements are believed more when the statements’
source is misattributed as originating from outside the exper-
imental setting, which may be interpreted as an external
validity cue. But even in this case, repeated statements that
are attributed to the artificial laboratory situation are still
believed more than nonrepeated statements (Arkes et al.,
1989; Law et al., 1998). Similar to source credibility, source
variability has been shown to influence the truth effect, but
only when participants are aware of the variability in sources
(Roggeveen & Johar, 2002). The effect appears to be more
pronounced when the statements’ source is not correctly
remembered but the statements’ content is (Law & Hawkins,
1997). Finally, older adults who tend to have impaired source
memory are especially susceptible to the truth effect (Law
et al., 1998; Skurnik et al., 2005; for differing results, see
Parks & Toth, 2006). Thus, a disconnection of content and
source memory seems to provide beneficial conditions for
the occurrence of the truth effect. This can be seen as func-
tional; for instance, it is plausible that familiar or recognized
information from a source that is not recalled—and thus not
evaluable—may be interpreted as a part of general semantic
knowledge and by this interpreted as probably true without
further evaluation (Law & Hawkins, 1997).
Taken together, research on the influence of feedback,
source characteristics, and age of participants on the truth
effect suggests ways in which different memory processes
are involved in the truth effect, above and beyond the explicit
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242 Personality and Social Psychology Review 14(2)
use of recognition and the implicit use of cognitive feelings
of discrepant fluency (that both are enhanced by repetition).
Perhaps most importantly, imprecise source memory may
support the effect. Therefore, repetition may affect truth rat-
ings in two opposite ways: First, repetition enhances the
cognitive processing fluency of statements; second, repeti-
tion also enhances the probability that both a statement’s
content and its source are stored in memory.
Focus of the Meta-Analysis
As discussed above, the nonreferential part of the repetition-
based truth effect is the product of two processes: An increase
in fluency and the subsequent experience of this increased
fluency as discrepant from a comparison standard. Importantly,
the second process is likely affected by the (homogeneous or
heterogeneous) judgment context; this contextual effect is
reflected in differences between the within- and between-
items criteria. It is an inherent limitation of the meta-analytic
method that these measures do not represent process-pure
indicators of the above context effects, and the present meta-
analysis cannot replace controlled experiments of such context
effects. Nevertheless, by focusing on the differences between
the within-items and the between-items components of the
truth effect, the present review can provide an initial assess-
ment of the role of the comparison standard as well as
contextual moderation of the truth effect, and it hopes to stim-
ulate experimental research in this direction.
The present review separately analyzes the between-items
and within-items truth effects and investigates possible dif-
ferential effects of procedural and participant variables on
both components. First, we investigate the overall effect of
repetition on subjective truth separately for both compo-
nents. Next, we examine whether the effect of repetition on
both components of subjective truth judgments is enhanced
or diminished by a number of procedural and participant
moderators that are of potential theoretical interest. Modera-
tors include characteristics of stimuli, presentation, and
measurement of the truth effect as well as levels of process-
ing, the number of repetitions, and participants’ age.
Method
Literature Search. We retrieved published articles, book
chapters, and dissertations through an extensive search in Psy-
cINFO, PubMed, and Web of Science, the main databases for
psychological literature. Furthermore, we searched in Pro-
Quest, the main database for doctoral dissertations, Google
Scholar, and two business literature databases (Business Source
Premier and EconLit) because a considerable amount of
research on the truth effect has been published in consumer
and marketing journals. The following keywords were used:
truth effect, illusory truth, and truth judgment(s). We also
searched Web of Science for articles that cited the first truth
effect article, by Hasher et al. (1977). We asked for unpub-
lished data through inquiries using the mailing lists of the
Society of Personality and Social Psychology and the Euro-
pean Association of Social Psychology (the former European
Association of Experimental Social Psychology).
Criteria for Inclusion. We applied the following criteria to
determine the eligibility of each study for inclusion in the
meta-analysis:
1. Studies that investigated the effect of repetition on
subjective ratings of truth were included.
2. Studies that reported means or proportions of sub-
jective truth ratings at least of new and repeated
statements in Session 2 (between-items criterion)
or of repeated statements at their first and second
(or more) presentation or judgment (within-items
criterion) were included. Studies that did not report
means or proportions of subjective truth judgments
were excluded (k = 13).
Furthermore, we avoided duplication by excluding data that
were reported in previously published work and that were
thus already included in the meta-analysis (k = 2). All studies
had an experimental or at least a quasi-experimental design.
After application of the exclusion criteria, 51 independent
studies matched the criteria and therefore were included in
the analysis.
Coding of Study Characteristics. Appropriate studies were
coded by the first and the third author, using a data cod-
ing form. Both authors were familiar with the truth effect
literature and discussed various preliminary versions of the
coding form before starting the coding. The topics of the
coded study characteristics can be grouped to the following
areas: (a) study and sample descriptors (e.g., year and type of
publication, type of sample, and proportion of male partici-
pants), (b) research design descriptors (e.g., the moderators
investigated), (c) procedure descriptors (e.g., delay between
assessments, characteristics of data collection), and (d) data-
level information (e.g., type of data reported). The relevant
variables are described in more detail below. The interrater
agreement was high: Of 456 ratings, 6 were divergent. These
differences were resolved through discussion.
Study and sample descriptors. Although we had no hypoth-
eses about influences of publication year, publication type,
gender, and sample size on the truth effect, we coded these
variables for descriptive reasons. Studies in journal articles
(k = 42) and book chapters (k = 1) were published between
1977 and 2006. Unpublished studies (doctoral dissertations,
k = 4; master’s theses, k = 1; and other manuscripts, k = 3)
were from 1998 to 2007. The sample sizes ranged from n = 12
to n = 145 participants (M = 46.78, Mdn = 40, SD = 25.59).
The gender of participants was rarely reported.
Furthermore, we recorded the type of sample used in the
studies (2 representative samples, 43 convenience samples
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Dechêne et al. 243
consisting of university students, and 6 quasi-experimental
studies that compared older and younger adults). Partici-
pants’ mean age was reported only in studies that investigated
the effect of age (Mold = 72.86, SD = 5.09; Myoung = 22.54,
SD = 4.11). Given the large proportion of student samples, it
can be assumed that participants’ mean age was similar to
that of the young participants in studies on age effects.
Research design descriptors. Categorizing the study designs
involved coding the type of moderator (e.g., level of process-
ing, age) that was investigated in a study. If the information
given did not allow for a definite coding judgment or the
study did not involve a moderator, the data were coded as
missing. In addition, we coded the type of dependent vari-
able used to measure the truth judgments (a 7-point
Likert-type scale was most frequently used; anchored either
with 1 = true and 7 = false or with 1 = false and 7 = true).
Procedure descriptors. Technical characteristics of the study
procedures were coded. These included the number of mea-
surements, the time of the measurements (e.g., at Sessions 1
and 2, only Session 2), the number of presentations of the
items, the modality of data collection (e.g., paper and pencil,
computer), the presentation mode of the items (e.g., visual or
auditory), and the response mode (e.g., written form, orally).
Furthermore, the delay between two sessions was coded (e.g.,
< 30 min, 1 day, 1 week) as well as the duration of presenta-
tion of one item, if this information was available. There was
always a category to indicate if there was no information
available or a different procedure was used.
In general, the coded variables can be categorized as either
procedural (e.g., stimulus variables, measurement variables)
or participant (e.g., age of participants, level of processing)
variables. At least one effect was coded from each study
(within-item criterion and/or between-item criterion). If a
study systematically investigated a variable of interest in this
meta-analysis, one effect for each level was coded if the
manipulation was between participants. We did not include
effects from manipulations that were implemented within par-
ticipants because they violate the assumption of independence
of the effect sizes. In this case, we collapsed over manipula-
tions (see Hedges & Olkin, 1985; Rosenthal & Rubin, 1986).
Meta-Analytic Procedure.
Calculating effect sizes. We used the standardized mean dif-
ference to estimate the influence of repetition on truth
judgments. The effect size d is a scale-free measure of the
difference of two group means (Cohen, 1988). We calculated
the effect sizes by using Hedges’s formula based on means
and pooled standard deviations:
g = (M1 – M2)/SDpooled. (1)
The pooled standard deviation was computed as,
SDpooled =
SD
n SD n SD
n n
pooled =
− + −
+ −
( ) ( ) .
1 1
2
2 2
2
1 1
2 (2)
We refrained from computing effect sizes from F tests, t
tests, and p values because of the repeated measures designs
typically used in truth effect experiments. The test statis-
tics of repeated measures designs use error terms that are
affected by the correlation between the measures: The larger
the correlation between the measures, the smaller the error
(and the larger the test statistic). If an effect size is computed
from such a statistic without taking the correlation between
the measures into account, the effect size will be overestimated
(Dunlap, Cortina, Vaslow, & Burke, 1996). Because none
of the studies reported the correlations, rendering adequate
corrections impossible, we used only the reported means and
standard deviations for the computation of the effect sizes.
Although this may imply somewhat less precise estimates, it
avoids potentially severe biases.
Twenty-one studies provided standard deviations for the
reported means; seven studies reported a range of standard
deviations. In the latter case, we computed the pooled stan-
dard deviations from the range. Where no standard deviations
were provided, we chose to impute the pooled standard devi-
ation from an overall estimate that was obtained from those
studies in which standard deviations were reported or could
be extracted.
A positive effect size indicates that truth ratings increase
with repetition. For the computation of the within-items cri-
terion effect size, we subtracted the mean of the first truth
rating from the mean of the repeated truth rating. We obtained
k = 32 independent effect sizes for the within-items criterion.
For the between-items criterion, we subtracted the mean
truth rating of new statements from the mean truth rating of
repeated statements. We obtained k = 70 independent effect
sizes of the between-items criterion.
We applied a small-sample correction on the effect sizes,
using the following formula (Hedges & Olkin, 1985):
dunbiased =
d g
N
unbiased = ×
−− −





13
4 2 1( ) . (3)
The resulting effect size d is unbiased by sample size and can
be interpreted following the conventions of Cohen (1988)
with d = .2 indicating a small effect, d = .5 indicating a
medium effect, and d = .8 indicating a large effect.
Calculation of average effect sizes. In computing average
effect sizes, individual study effect sizes were weighted by
the inverse of their variance. This procedure lends greater
weight to studies with more precise effect size measures (e.g.,
because of larger samples, stricter experimental control, etc.)
and thereby ensures that the meta-analytic results are not
easily distorted by outcomes from a single small study.
Tests for moderation. We used homogeneity analyses to test
for moderation (Cooper & Hedges, 1994; Hedges & Olkin,
1985). In these analyses, the amount of variance in an observed
set of effect sizes is compared to the amount of variance that
would be expected by sampling error alone. The null hypothesis
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244 Personality and Social Psychology Review 14(2)
of homogeneity (i.e., no variation across effect sizes) is
tested using a within-class goodness-of-fit statistic, Qw,
which has an approximate chi-square distribution with k – 1
degrees of freedom, where k equals the number of effect
sizes (Hedges & Olkin, 1985). A significant Qw statistic indi-
cates heterogeneity, that is, a systematic variation among
effect sizes; such a finding would suggest that other vari-
ables moderate the effect (Cooper, 1998).
Homogeneity analyses can be used in a similar way to test
whether groups of average effect sizes vary more than pre-
dicted by sampling error. The null hypothesis of no variation
across groups can be tested by computing a between-class
goodness-of-fit statistic, Qb. It has a chi-squared distribution
with j – 1 degrees of freedom, where j equals the number of
tested groups. If the Qb statistic is significant, average effect
sizes vary between the categories of the moderator more than
predicted by sampling error. This procedure is similar to an
analysis of variance that tests for group mean differences or
to a multiple regression model that tests for linear effects.
Fixed versus random error models. It is debated whether a
fixed-effects (FE) model or a random-effects (RE) model is
more adequate for meta-analyses of effect sizes (e.g.,
Schmidt, Oh, & Hays, 2009). On one hand, FE models are
more powerful and therefore more likely to detect effects of
moderators. On the other hand, they tend to be more liberal
and reject the null hypothesis more often than indicated by
the nominal alpha level when the true effect is zero. FE
models are thought to be appropriate when an inference is
made only about the sample of studies under investigation,
whereas RE models are the appropriate method when the
goal is to generalize the findings across all possible studies.
We fitted both models in the present study for the following
reasons. First, there is no consensus yet as to which method
should generally be preferred. Second, where the results of
both analyses diverge, both can be important: We are inter-
ested in the effects of a given moderator on the present
sample of studies but also whether the effects of that modera-
tor can be generalized.
Analyses followed the methods introduced by Hedges
(1983; Hedges & Olkin, 1985; Hedges & Vevea, 1998; also
see Raudenbush, 1994), as implemented for SPSS by Lipsey
and Wilson (2001; also see http://mason.gmu.edu/~dwilsonb/
ma.html).
Results
Prior to analyses, we checked the distribution of uncorrected
effect sizes for outliers. No outliers were indicated by the
box plot. We also checked the distribution of uncorrected
effect sizes for possible publication bias. As indicated by
funnel plots for both the within-items and the between-items
criteria, effect sizes are distributed symmetrically, and thus
publication bias does not seem to be a problem.
Overall Analyses
In a first step, analyses of the truth effect for all independent
effect sizes (32 within items, 70 between items) that were
retrieved from 51 studies were separately performed for both
components of the effect, collapsing across procedural and
participant variables.
Results of overall analyses for both criteria show that
both weighted-average ds differ from zero (see Table 1). Fol-
lowing the conventions of Cohen (1988), both components
of the truth effect are medium-sized effects under both
FE and RE assumptions: The effects ranged from d = –.28 to
.89 for the within-items criterion and from d = –.18 to 1.43
for the between-items criterion.
Descriptively, the within-items effect was smaller than
the between-items effect, and we tested whether this differ-
ence was substantial. Note that, when computed for the same
study, the within- and the between-items effects are not indepen-
dent in two ways: (a) The data are based on the same sample
because of the repeated measures designs and (b) the mean
subjective truth rating of repeated items in Session 2 is used
to compute both effect sizes. To avoid a violation of indepen-
dence, we chose to compare effect sizes of the within-items
criterion with effect sizes of the between-items criterion only
for those studies that did not report a within-items criterion.
Thus, we excluded between-items effect sizes from analyses
that were derived from studies that reported both criteria.
Results of the inverse variance weighted one-way ANOVA
with a FE model show that, in fact, the within-items criterion
is smaller (FE: dwithin = .39; 95% confidence interval [CI] =
0.32, 0.47; k = 32) than the between-items criterion (dbetween =
.52; 95% CI = 0.46, 0.58; k = 41), Qb(df = 1) = 6.21, p = .01.
When a RE model was applied, the difference between both
Table 1. Overall Meta-Analytic Results for Within- and Between-Items Criterion
95% Confidence Interval
Criterion k d Low Estimate High Estimate z Qw
Within items 32 .39*** (.39)*** 0.32 (0.30) 0.47 (0.49) 10.33 (8.08) 47.21*
Between items 70 .49*** (.50)*** 0.45 (0.43) 0.55 (0.57) 19.67 (13.41) 142.04***
Note: Fixed-effects estimates are presented outside parentheses, and random-effects estimates are within parentheses.
*p < .05. ***p < .0001.
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Dechêne et al. 245
criteria was only marginally significant (RE: dwithin = .39;
95% CI = 0.28, 0.51; k = 32; dbetween = .53; 95% CI = 0.44,
0.62; k = 41), Qb(df = 1) = 3.29, p = .07. This indicates that,
in fact, in the given set of studies both criteria differ in mag-
nitude. As the results from the RE model suggest, however,
this result should probably not be generalized to all possi-
ble studies on the truth effect. Also note that the sample of
effect sizes of the between-items criterion used in this com-
parison differed from the overall set and that the effect
size of this subsample was greater than that of the overall
sample in both models; perhaps those studies that did not
examine the within-items criterion systematically differ from
those that did (see Wilson, 2003, for a discussion of con-
founds in meta-analysis).
We applied homogeneity analyses on both criteria. The
results indicate heterogeneity for both the within-items and
the between-items criteria (see Table 1). Thus, it is likely
that both components of the effect are moderated by other
variables. We performed all moderator analyses separately
for both criteria. Analyses are grouped into (a) procedural
variables that represent characteristics of the stimuli, the
presentation, and measurement variables and (b) participant
variables that include the age of the sample, the level of
processing, and the influence of further (i.e., more than one)
repetitions on the truth effect. For some participant vari-
ables, there was too little information given in the studies to
include them in the analysis (e.g., gender of participants,
individual differences).
Moderator Analyses
Stimulus Variables. Two possible procedural moderators
can be characterized as variables of the stimuli: (a) whether
statements are repeated verbatim or only the gist of a statement
is repeated and (b) whether the proportion of critical items in
the overall pool of presented items in the studies influences
the effect. Both are of theoretical interest to understand the
mediating processes of fluency and discrepancy on the occur-
rence of the truth effect. For instance, a gist repetition may
affect the fluency of a statement (i.e., it is experienced as
relatively disfluent as compared to a verbatim repetition).
Similarly, a higher proportion of repeated items in a set of
statements may reduce the experienced discrepancy against
relatively disfluent statements and thereby may reduce the
magnitude of the effect.
Verbatim versus gist repetition. We examined whether the
statements in experiments were repeated verbatim or whether
the gist of the statement was repeated. For example, Arkes
and colleagues (1991, Experiment 2) presented text passages
about China in a first session and repeated passages contain-
ing the same facts as in the text presented first (i.e., they used
a gist repetition). As a result, the China-related statements
were rated more probably true as compared to a control con-
dition that had not seen the text about China before.
Moderator analyses for changes in wording (gist vs. ver-
batim repetition) from Session 1 to Session 2 were separately
performed for the within-items and the between-items crite-
rion; results are shown in Table 2. Unfortunately, only two
effect sizes were available in the gist group for the within-
items criterion; results of the Qb statistic on the within-items
criterion can therefore not be reasonably interpreted. We present
the results for descriptive reasons only. For the between-items
criterion, effects of gist repetition were significantly smaller
than those of verbatim repetition under both an FE and an
RE model. Interestingly, in the RE analysis, the truth effect
from gist repetition did not reach significance. The results
suggest that repeating a statement in a different wording than
in the first presentation diminishes the truth effect or may even
eliminate it.
Proportion of critical items. We examined whether the pro-
portion of critical (i.e., repeated) items in the total number of
items judged affects the size of the truth effect. Although this
proportion varied enormously (i.e., between 18% and 100%),
it was 50% in more than half of the cases. As the discrepancy
between fluent versus disfluent stimuli is discussed as an
important mediator, the proportion of fluent versus disfluent
stimuli may be relevant (Dechêne et al., 2009; Hansen et al.,
2008). For instance, a higher proportion of disfluent (i.e.,
nonrepeated) stimuli may lead to greater truth effects by
enhancing or strengthening the experienced discrepancy to
Table 2. Results of Moderator Analysis Examining the Effect of Change of Wording on Both Components of the Truth Effect
95% Confidence Interval
Type of Repetition k d Low Estimate High Estimate Qb(df = 1)
Within-items criterion < 1 (< 1)
Verbatim repetition 30 .39*** (.39)*** 0.32 (0.29) 0.47 (0.49)
Gist repetition 2 .40† (.40) -0.44 (-0.09) 0.85 (0.89)
Between-items criterion 13.35** (5.95)*
Verbatim repetition 64 .53*** (.53)*** 0.47 (0.46) 0.58 (0.60)
Gist repetition 6 .21* (.22)† 0.05 (-0.02) 0.37 (0.46)
Note: Fixed-effects values are presented outside parentheses, and random-effects values are within parentheses.
†p < .10. *p < .05. **p < .001. ***p < .0001.
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246 Personality and Social Psychology Review 14(2)
fluent (i.e., repeated) stimuli. Regression analyses revealed
that the proportion of critical items affects neither the within-
items criterion, FE: Qb(df = 1) < 1, RE: Qb(df = 1) < 1, nor the
between-items criterion, FE: Qb(df = 1) < 1, RE: Qb(df = 1) <
1. However, given the reduced range of variability, this null
finding should not be overinterpreted.
Presentation Variables. Presentation variables include the
presentation time per statement, the delay between Sessions 1
and 2, the modality of the presentation (i.e., whether state-
ments were presented to the participants visually, auditory,
or mixed), and whether the repeated statements in Session 2
were presented to participants homogenously (i.e., in a context
without new statements) or heterogeneously (i.e., interspersed
with new statements).
Presentation time per statement. In all, 22 studies did not
specify the presentation time per statement and therefore were
excluded from analysis; for the within-items criterion, k = 24
were included, and for the between-items criterion, k = 48
were included. We decided to group the available presentation
times in three categories because this yielded meaningful and
sufficiently large categories: less than or equal to 8 s per state-
ment, more than 8 s per statement, and participant paced.
Presentation time per statements did not affect either crite-
rion in FE and RE models (see Table 3). We conducted
follow-up analyses for the within-items criterion and tested
whether a presentation time less or equal to 8 s produced sig-
nificantly greater effects as compared to presentation times
more that 8 s. No differences were found using FE or RE
models, FE: Qb(df = 1) = 1.08, p = .29; RE: Qb(df = 1) = 1.08,
p = .29. This result corresponds with the finding of Gigerenzer
(1984), who experimentally varied whether each statement
had to be judged within 5 s versus 10 s and found no difference
between these intervals. On a descriptive level, participant-
paced presentation seems to produce the smallest effects.
Delay between sessions. Brown and Nix (1996) and
Gigerenzer (1984) investigated whether different delays
between the sessions affect the truth effect. Gigerenzer varied
the delay between sessions (1 vs. 2 weeks). No influence
of intersession interval was found. Similarly, Brown and
Nix varied whether Session 2 was administered 1 week, 1
month, or 3 months after Session 1; they found no difference
in the truth effect for true items. Repeated false items, how-
ever, were rated less true than new (also false) items after a
1-week interval; no such difference was found for the
1-month or the 3-month conditions. Thus, experimental evi-
dence so far shows no clear pattern for the influence of
intersession interval on the truth effect. Along the same lines,
many studies that did not directly examine the influence of
the intersession interval obtained the truth effect with delays
ranging from no more than minutes (e.g., Arkes et al., 1989;
Begg & Armour, 1991; Schwartz, 1982) to several weeks (e.g.,
Bacon, 1979; Hasher et al., 1977).
For 20 studies, the length of the delay between the ses-
sions was not specified, and therefore these effect sizes were
excluded from the analysis. For the between-items criterion,
51 cases were included (k = 19 excluded), for the within-
items criterion 30 cases were included (k = 2 excluded).
As shown in Table 4, both criteria were not moderated by the
delay between the sessions in both models, between-items
criterion FE: Qb(df = 2) = 0.66, p = .72; RE: Qb(df = 2) = 0.35,
p = .84; within-items criterion FE: Qb(df = 2) = 3.45, p = .18;
RE: Qb(df = 2) = 2.75, p = .25. On a descriptive level, the
effects size of the within-items criterion was very small when
Session 2 was administered on the same day as Session 1. For
practical reasons, researchers often tend to realize Session 2
either within the same day or within a week after Session 1.
Thus, we conducted additional analyses that compared effect
sizes of within-day studies with those of the within-week
type. As suggested by a marginally significant effect in the
fixed-error model, administering both sessions within the same
day (dwithin = .25; 95% CI = 0.07, 0.43; p < .05) tends to yield
smaller effect, as compared to when the second session is
administered at least 1 day after the first (dwithin = .44; 95%
CI = 0.31, 0.67; p < .0001), FE: Qb(df = 2) = 2.91, p = .08.
However, this effect does not replicate in a random-error
model (within day: dwithin = .25; 95% CI = 0.07, 0.43, p = .01;
Table 3. Results of Moderator Analysis on Statements’ Presentation Time for Within- and Between-Items Criterion
95% Confidence Interval
Presentation Time
per Statement k d Low Estimate High Estimate Qb(df = 2)
Within-items criterion 3.78 (2.85)
≤ 8 s 3 .55*** (.55)** 0.29 (0.25) 0.82 (0.85)
> 8 s 4 .38*** (.38)** 0.20 (0.16) 0.56 (0.61)
Participant paced 17 .28*** (.27)*** 0.17 (0.07) 0.39 (0.41)
Between-items criterion 5.25† (1.30)
≤ 8 s 5 .49*** (.51)** 0.27 (0.21) 0.71 (0.82)
> 8 s 27 .54*** (.53)*** 0.46 (0.41) 0.62 (0.65)
Participant paced 16 .38*** (.41)*** 0.27 (0.24) 0.49 (0.58)
Note: Fixed-effects values are presented outside parentheses, and random-effects values are within parentheses.
†p < .10. **p < .001. ***p < .0001.
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Dechêne et al. 247
within week: dwithin = .45; CI 95% = 0.30, 0.59, p = .0001),
Qb(df = 2) = 2.57, p = .11). A tendency toward a smaller
within-items effect for statements that were shown on the
same day could be explained by a higher proportion of par-
ticipants who remembered their first truth judgment for the
respective statements; they might not have shown a strong
increase in subjective truth for the second judgment because
of a desire for consistency.
Modality of presentation. The truth effect has been reported
with visual (e.g., Arkes et al., 1989; Begg et al., 1992;
Hawkins & Hoch, 1992), with auditory (Gigerenzer, 1984;
Hasher et al., 1977), and with mixed (i.e., visually and audi-
tory; Bacon, 1979; Begg & Armour, 1991) presentations. It
is yet unclear whether modality of presentation systemati-
cally influences the truth effect. Four studies did not specify
the modality of presentation and therefore were excluded
from analyses, leaving k = 28 effect sizes for the analysis of
the within-items criterion and k = 66 for the analysis of the
between-items criterion. Results (see Table 5) show that the
truth effect is not affected by modality (the within-items cri-
terion results for mixed presentation have to be interpreted
with caution because of the small number of effect sizes).
Homogenous versus heterogeneous context. In most studies
the truth effect has been examined in heterogeneous lists of
mixed and repeated statements; it has rarely been studied in
homogeneous lists (Dechêne et al., 2009; Schwartz, 1982).
Results of the moderator analysis on the available effect
sizes of these different list types are presented in Table 6.
Unfortunately, Qb statistics for the between-items criterion
could not be computed because only one case of a homoge-
neous list was reported. More studies are certainly needed to
investigate the truth effect under homogeneous presentation
conditions. The results for the within-items criterion suggest
that the truth effect may be reduced in a homogeneous con-
text. This finding provides initial support for the important
role of context in determining comparison standards
(Dechêne et al., 2009; Hansen et al., 2008).
Measurement Variables.
Scale. We examined whether the scale used to measure the
truth ratings influences the truth effect. Most studies (k = 26)
used a 7-point Likert-type scale with values ranging from
false (1) to true (7). Ten studies used a 7-point scale with
values from true (1) to false (7). Three studies used a 6-point
scale (higher values indicated higher truth ratings). Five
Table 4. Results of Moderator Analysis of Delay Between Sessions on Within- and Between-Items Criterion
95% Confidence Interval
Session 2 Administered k d Low Estimate High Estimate Qb(df = 2)
Within-items criterion 3.44 (2.74)
Within day 9 .25* (.24)* 0.07 (0.04) 0.43 (0.46)
Within week 11 .44*** (.45)*** 0.31 (0.29) 0.57 (0.61)
Longer delay 10 .44*** (.45)*** 0.32 (0.28) 0.56 (0.61)
Between-items criterion < 1 (< 1)
Within day 25 .48*** (.49)*** 0.39 (0.37) 0.57 (0.62)
Within week 14 .43*** (.44)*** 0.32 (0.28) 0.54 (0.59)
Longer delay 12 .48*** (.49)*** 0.36 (0.32) 0.59 (0.65)
Note: Fixed-effects values are presented outside parentheses, and random-effects values are within parentheses.
*p < .05. ***p < .0001.
Table 5. Results of Moderator Analysis on Presentation Modality for Within- and Between-Items Criterion
95% Confidence Interval
Presentation Mode k d Low Estimate High Estimate Qb(df = 2)
Within-items criterion < 1 (< 1)
Visual 21 .43*** (.43)*** 0.32 (0.32) 0.53 (0.53)
Auditory 5 .43** (.43**) 0.22 (0.22) 0.63 (0.63)
Mixed 2 .40** (.40**) 0.17 (0.17) 0.63 (0.63)
Between-items criterion 2.66 (1.01)
Visual 38 .51*** (.52)*** 0.44 (0.42) 0.58 (0.61)
Auditory 24 .51*** (.52)*** 0.43 (0.39) 0.61 (0.64)
Mixed 4 .68*** (.67)*** 0.48 (0.38) 0.87 (0.95)
Note: Fixed-effects values are presented outside parentheses, and random-effects values are within parentheses. The fixed-effect and the random-effect
model revealed the same results in the analysis of the within-items criterion because the random error variance component was zero.
**p < .001. ***p < .0001.
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248 Personality and Social Psychology Review 14(2)
studies used a continuous 16 cm scale with higher values
indicating higher truth rating. Finally, 6 studies used a
dichotomous measure. Only a single study used a 9-point
scale (false to true); it was not included in this analysis.
Results (see Table 7) suggest that the scale used to measure
truth ratings influences both components of the truth effect.
This finding was replicated in FE and RE models. For the
within-item criterion, results suggest that a 6-point scale
evokes a larger effect as compared to a 7-point scale. This is
indeed the case, as indicated by a follow-up test, FE: Qb(df =
1) = 7.65, p < .05; RE: Qb(df = 1) = 5.75, p < .05.
Results for the between-items criterion suggest that the
widely used 7-point scale from false to true evokes smaller
effects than do the other scales. A follow-up analysis revealed
that this difference was significant, FE: Qb(df = 1) = 23.57, p <
.001; RE: Qb(df = 1) = 10.52, p = .001. Effect sizes obtained
using dichotomous responses do not differ from those collected
on the other scales, FE: Qb(df = 1) < 1; RE: Qb(df = 1) < 1.
It has been discussed whether scales with a midpoint
(i.e., odd scales) are superior to scales without one (i.e., even
scales), or vice versa (e.g., Krosnick, 1991; Krosnick &
Fabrigar, 1997). Even scales force the participant to choose
a clear direction of judgment, whereas odd scales allow
participants to choose an indifference point. Thus, we were
interested to determine whether the truth effect can be captured
better by an even scale that may foster the use of fluency
Table 6. Results of Moderator Analysis of Homogenous Versus Heterogeneous Presentation for Within- and Between-Items Criterion
95% Confidence Interval
List Type k d Low Estimate High Estimate Qb(df = 1)
Within-items criterion 5.65* (4.44)*
Heterogeneous 29 .42*** (.43)*** 0.35 (0.33) 0.50 (0.52)
Homogeneous 3 .08 (.07) -0.20 (-0.24) 0.35 (0.39)
95% Confidence Interval
List Type k d Low Estimate High Estimate Qb
Between-items criterion —
Heterogeneous 65 .53*** (.51)*** 0.48 (0.44) 0.58 (0.58)
Homogeneous 1 -.09 (-.09) -0.62 (-0.76) 0.43 (0.55)
Note: Fixed-effects values are presented outside parentheses, and random-effects values are within parentheses.
*p < .05. ***p < .0001.
Table 7. Results of Moderator Analysis of Scale Type on Within- and Between-Items Criterion
95% Confidence Interval
Scale k d Low Estimate High Estimate Qb(df = 2)
Within-items criterion 7.94* (6.00)*
1–7 (false–true) 23 .33*** (.33)*** 0.24 (0.22) 0.43 (0.44)
1–7 (true–false) 2 .40** (.41)** 0.18 (0.12) 0.63 (0.69)
1–6 (false–true) 6 .62*** (.62)*** 0.44 (0.42) 0.79 (0.82)
16 cm (false–true) —
Dichotomous —
95% Confidence Interval
Scale k d Low Estimate High Estimate Qb(df = 4)
Between-items criterion 24.50** (11.27)*
1–7 (false–true) 40 .39*** (.41)*** 0.32 (0.32) 0.45 (0.49)
1–7 (true–false) 12 .64*** (.65)*** 0.53 (0.49) 0.74 (0.79)
1–6 (false–true) 6 .66*** (.65)*** 0.48 (0.43) 0.83 (0.88)
16 cm (false–true) 5 .66*** (.65)*** 0.49 (0.42) 0.83 (0.89)
Dichotomous 7 .54*** (.53)** 0.32 (0.27) 0.75 (0.79)
Note: Fixed-effects values are presented outside parentheses, and random-effects values are within parentheses.
*p < .05. **p < .001. ***p < .0001.
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Dechêne et al. 249
more than an odd scale. We grouped effect sizes into the two
categories (i.e., both variants of the 7-point scale and the
9-point scale were classified as odd; the 6-point scale and the
dichotomous responses were classified as even; the 16 cm
scale was excluded because it cannot be categorized as odd
vs. even). Results (see Table 8) show that measuring truth
judgments with an even scale yields greater effects on both
criteria. Note that, in the RE model, the scales do not signifi-
cantly differ for the between-items effect.
Modality of experiment and data collection. We examined
whether the data collection mode, that is, paper and pencil
(k = 30 studies) versus computer (k = 11 studies), influences
the truth effect. Ten studies did not report mode of data col-
lection, and it was not possible to infer the mode of data
collection that was used; these studies were excluded from
analysis. Unfortunately, there were again too few within-
items effect sizes in one condition (computer collection); the
results are given for descriptive reasons. Results of both
models (see Table 9) show that the modality of data collec-
tion affects the between-items effect: Conducting a truth
effect experiment on the computer produces smaller effects
than with paper and pencil. The reasons for this effect are
unclear, and we can only speculate that there may be con-
founds with restricted presentation times in this analysis or
differences in the presentation of statements (i.e., sequen-
tially vs. all statements on the same sheet) that may foster or
diminish the experience of discrepant fluency. However,
other reasons are also possible, and further research is needed
on this point.
Other Variables. Beyond procedural aspects, other variables
may also affect the size of the truth effect and may function
differentially on the processes that are involved in the occur-
rence of the within- and the between-items effect. Research
has concentrated on cognitive processing styles and
memory processes. Level of cognitive processing was mainly
examined by manipulation of high versus low involvement
or cognitive load. Participants’ age was investigated because
it may indirectly reflect the influence of memory on the
truth effect because older adults tend to have impaired
memory capacities. Furthermore, we conducted analyses on
the influence of more than one repetition of statements on
the truth effect. Other variables, such as individual judg-
ment or processing styles (e.g., need for cognition, faith in
intuition), were examined so infrequently that we were not
able to investigate them here.
Level of Processing. An important question in research on
the truth effect is whether the effect is moderated by level
of processing. Hawkins and Hoch (1992) manipulated in
Session 1 whether participants had to judge comprehensi-
bility (i.e., a low involvement manipulation) or subjective
truth (i.e., high involvement) of consumer-related claims and
found that the truth effect (indicated by the between-items
Table 8. Results of Moderator Analysis of Scale Type (Odd vs. Even) for Within- and Between-Items Criterion
95% Confidence Interval
Scale k d Low Estimate High Estimate Qb(df = 1)
Within-items criterion 7.61* (5.91)*
Odd 26 .35*** (.34)*** 0.26 (0.25) 0.43 (0.44)
Even 6 .62*** (.62)*** 0.45 (0.42) 0.79 (0.82)
Between-items criterion 4.03* (1.65)
Odd 52 .46*** (.47)*** 0.40 (0.38) 0.52 (0.55)
Even 13 .61*** (.60)*** 0.47 (0.42) 0.75 (0.78)
Note: Fixed-effects values are presented outside parentheses, and random-effects values are within parentheses.
*p < .05. ***p < .0001.
Table 9. Results of Moderator Analysis of Data Collection Modality for Within- and Between-Items Criterion
95% Confidence Interval
Data collection modality k d Low Estimate High Estimate Qb(df = 1)
Within-items criterion < 1 (< 1)
Paper and pencil 21 .42*** (.43)*** 0.33 (0.31) 0.54 (0.55)
Computer 2 .27 (.21) -0.32 (-0.34) 0.73 (0.53)
Between-items criterion 17.74*** (7.21)*
Paper and pencil 42 .59*** (.59)*** 0.53 (0.51) 0.66 (0.69)
Computer 14 .30*** (.33)** 0.18 (0.16) 0.43 (0.50)
Note: Fixed-effects values are presented outside parentheses, and random-effects values are within parentheses.
*p < .05. **p < .001. ***p < .0001.
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250 Personality and Social Psychology Review 14(2)
criterion) was larger under the low involvement condition
(also see Hawkins, Hoch, & Meyers-Levy, 2001). In follow-
ing this classification, the task of performing truth judgments
at Session 1 was coded as a high level of processing, whereas
merely reading the statements, or performing other superfi-
cial tasks, was coded as a low level of processing. A levels of
processing effect is supported by the results of the moderator
analyses (see Table 10), showing that the truth effect on the
between-items criterion is increased with low as compared to
high levels of processing at Session 1. Note that this modera-
tor analysis cannot be performed for the within-items
criterion because (with one exception) all studies imple-
mented the level of processing manipulation in Session 1 and
did not obtain the necessary Session 1 truth ratings for the
low level of processing condition.
Age of Participants. The mean age of young participants
was M = 22.54 (SD = 4.11) and M = 72.86 (SD = 5.09) for
older participants. Note that only studies that directly inves-
tigated the influence of age on the truth effect reported the
age of the sample. However, most studies use student sam-
ples, suggesting a mean age between 18 and 30 years; thus,
we included these studies in the group of younger partici-
pants. Law and colleagues (1998) found that older adults
were especially susceptible to show the truth effect, espe-
cially after a longer delay (Skurnik et al., 2005). However,
there are also findings that show no differences in the truth
effect between old and young participants in a fluency
manipulation (Parks & Toth, 2006). Data were not available
for the within-items criterion. Descriptively, the truth effect
was larger for older adults (see Table 11); however, results of
the moderator analysis suggest that the truth effect is not
dependent on participants’ age.
Further Repetitions. Hasher and colleagues (1977) tested
whether, after an initial repetition, truth ratings continue to
be affected by further repetitions. Unfortunately, very few
effect sizes were available for both criteria, and therefore the
Qw statistic cannot be reasonably interpreted (within-items
criterion) or even computed (between-items criterion). Nev-
ertheless, there appears to be a tendency for an effect of
further repetitions on the between-items criterion: Mean
effect sizes of a second repetition were not different from
zero for the within-items criterion but were significantly dif-
ferent from zero for the between-items criterion (see Table 12).
Also, descriptively, the effects of a second and third repetition
were very small for the within-items criterion; in contrast,
the magnitude of the between-items criterion remained con-
stant beyond the first repetition.
Summary
Overall, the truth effect was of medium size. The effect was
moderated by response format and presentation duration but
not by modality of presentation or the proportion of critical
(i.e., repeated) statements. The truth effect was smallest on
the widely used 7-point Likert-type scale (1 = false, 7 =
true), and it was larger when an even scale was used (d = .61)
as compared to an odd scale (d = .46). The effect tended to
be moderated by statements’ presentation time, such that
participant-paced presentation tended to yield smaller effects
as compared to experimenter-paced presentation. The truth
Table 10. Results of Moderator Analysis of Level of Processing at Session 1 for Between-Items Criterion
95% Confidence Interval
Level of Processing k d Low Estimate High Estimate Qb(df = 1)
Between-items criterion 12.88** (4.35)*
High 51 .44*** (.45)*** 0.37 (0.37) 0.49 (0.54)
Low 19 .63*** (.62)*** 0.54 (0.49) 0.72 (0.75)
Note: Fixed-effects values are presented outside parentheses, and random-effects values are within parentheses.
*p < .05. **p < .001. ***p < .0001.
Table 11. Results of Moderator Analysis of Age of Participants for Between-Items Criterion
95% Confidence Interval
Age k d Low Estimate High Estimate Qb(df = 1)
Between-items criterion 1.51 (0.79)
Young 66 .49*** (.49)*** 0.44 (0.42) 0.54 (0.57)
Old 4 .64*** (.64)** 0.41 (0.33) 0.88 (0.96)
Note: Fixed-effects values are presented outside parentheses, and random-effects values are within parentheses.
**p < .001. ***p < .0001.
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Dechêne et al. 251
effect did not depend on the modality (auditory, visual, or
mixed) of the statements’ presentation. The proportion of
repeated items on the overall set of judged statements also
did not influence the effect.
A few additional moderators could be investigated only
for between-items effect sizes (there were too few relevant
within-items effect sizes). The truth effect was greater under
lower (d = .63) as compared to higher (d = .44) levels of
processing at Session 1. The effect was further moderated by
the data collection modality: A paper and pencil procedure
(d = .59) yielded a larger effect as compared to a computer-
based procedure (d = .30).
Last but not least, the truth effect was larger for the
between-items (d = .49) than for the within-items criterion
(d = .39), a finding that is consistent with the notion that they
may reflect different underlying processes. This notion is fur-
ther supported by moderator analyses: As summarized below,
the within-items and the between-items criteria were differ-
ently affected by a subset of the investigated moderators.
Within-Items Criterion. The within-items truth effect was
moderated by the delay between sessions: When Session 2
was administered on the same day as Session 1, a signifi-
cantly smaller effect (d = .25) was observed, as compared to
when a longer delay was used (d = .44). The within-items
truth effect was not affected by a verbatim (d = .39) versus
gist (d = .40) repetition. A within-items truth effect was not
found with a homogeneous test list (d = .08), but only with a
heterogeneous list of old and new statements in Session 2
(d = .42). Descriptively, additional repetitions (i.e., two or three
repetitions) did not reveal a considerable truth effect on the
within-items criterion (ds = .16).
Between-Items Criterion. The results obtained for the
between-items criterion differed from those obtained for the
within-item criterion with regard to the two moderators of delay
and verbatim versus gist repetition. In contrast to the within-
items effect, the delay between sessions did not influence
the between-items effect. Also, in contrast to the within-items
effect, the between-items effect was moderated by verbatim
versus gist repetition: The effect was larger with a verbatim
(d = .53) as compared to a gist (d = .21) repetition. Finally, and
again in contrast to the within-items criterion, the effect of the
second and subsequent repetitions on the between-items cri-
terion was still of considerable size (d = .44), descriptively,
and comparable to the effect of the first repetition.
Discussion
In summary, some general conclusions can be drawn. First,
the truth effect is of medium size (with CIs ranging between
d = .32 and d = .55, depending on the choice of criterion and
type of analysis). Second, the effect is robust against varia-
tions in presentation duration and modality, the proportion of
repeated statements, and participants’ age. Third, the effect is
smaller for scales that offer an indifference point (i.e., scales
with an odd number of points). These findings are consistent
with the widely held view that repetition, largely via the
subtle cues provided by increased processing fluency, affects
truth judgments in a wide range of situations. Before we turn
to comparing the within- and between-items effects, some addi-
tional findings are discussed: the levels of processing effect
and the role of interindividual differences.
Levels of Processing
The between-items truth effect was larger under low as com-
pared to high levels of processing, that is, shallower cognitive
processing during the statement’s first encounter led to a
more pronounced truth effect. Hawkins and Hoch (1992)
argued that high levels of processing foster more elaborative
thoughts about the statements; such elaborations are likely to
have a stronger influence on subsequent truth judgments than
low-level heuristic cues such as fluency. In contrast, people
who engaged in shallower cognitive processing are less
likely to elaborate; their judgments tend to be based more on
peripheral heuristic cues such as a statement’s familiarity (e.g.,
Hawkins & Hoch, 1992; Hawkins et al., 2001) or, we might
add, its fluency. Note that the present results are restricted to
effects of level of processing at the first encounter of a state-
ment; there is a paucity of research on the influences of level
of processing at the time of judgment.
Table 12. Overall Analyses of Effect Sizes for Second and Third Repetition for Within- and Between-Items Criterion
95% Confidence Interval
k d Low Estimate High Estimate z Qw
Within-items criterion
Second repetition 7 .16† (.17)† –0.01 (–0.03) 0.33 (0.37) 1.93 (1.65) 8.52
Third repetition 2 .16 (.16) –0.08 (–0.08) 0.41 (0.41) 1.28 (1.28) 0.02
Between-items criterion
Second repetition 6 .44*** (.48)** 0.26 (0.22) 0.63 (0.73) 4.76 (3.68) 9.01
Third repetition 1 .68** (—) 0.35 (—) 1.02 (—) 4.04 (—) —
Note: Fixed-effects values are presented outside parentheses, and random-effects values are within parentheses.
†p < .10. **p < .001. ***p < .0001.
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252 Personality and Social Psychology Review 14(2)
The levels of processing effect is reminiscent of research
on the “Spinozan” account introduced by Gilbert and col-
leagues (Gilbert, Krull, & Malone, 1990; Gilbert, Tafarodi, &
Malone, 1993). This account holds that “seeing is believing”:
When information is encoded, it is automatically and effort-
lessly “tagged” as true; elaborative processes are required to
modify this tag. If elaboration is not possible—for example,
under time pressure or cognitive load—people tend to encode
false information as true, even if it was explicitly identified
as false (Gilbert et al., 1993). Thus, similar to the present
result that low levels of processing facilitate the truth effect,
Gilbert and colleagues have shown that conditions of effortless
or superficial cognitive processing facilitate the acceptance
of new information as true.
Note that the Spinozan account does not distinguish between
effects on encoding versus judgment because it is not con-
cerned with the effects of repetition. To investigate levels
of processing effects on the experience (and use) of fluency
during truth judgments, future research should concen-
trate on the influence of level of processing at the time of the
judgment.
Individual Differences
As revealed by the present meta-analysis, there is a lack of
research on the influence of individual differences on the
truth effect. It is plausible that individuals’ predispositions
such as general skepticism (e.g., Hurtt, 1999; Obermiller &
Spangenberg, 1998) or the tendency toward an intuitional–
experiential thinking style (e.g., Epstein, Pacini, Denes-Raj,
& Heier, 1996) may influence their susceptibility to the truth
effect: Individuals with a highly intuitive style of thinking
may be more sensitive to their metacognitive experiences, such
as processing fluency, and may therefore exhibit a stronger
truth effect. In contrast, people with a greater tendency to dis-
play general skepticism may be less susceptible to the truth
effect. Given that the present meta-analytic review has firmly
established the existence of a substantial, robust, medium-sized
effect, future research focusing on individual differences is
undoubtedly worthwhile.
Two Components of the Truth Effect
We now turn to discussing the differences between the between-
and within-items effects in terms of contextual effects on
the comparison standard. But first, let us again point out an
important limitation of the meta-analytic findings: Almost
all studies implemented a heterogeneous context with both
repeated and nonrepeated statements, from which both the
between-items and most of the within-items effect sizes were
computed for the present analyses; only a small number of
studies used the homogeneous context (for these studies,
only the within-items criterion was computed). As a conse-
quence, there is considerable overlap between the processes
that determine the between- and within-items effects; they
cannot be interpreted as reflecting distinct cognitive processes.
As we pointed out above, it is not possible to purely disen-
tangle underlying cognitive processes using the meta-analytic
method. Such an effort to disentangle the underlying processes
requires the use of controlled experiments, preferably in com-
bination with comprehensive formal models of the truth effect
(e.g., Unkelbach & Stahl, 2008).
Despite these limitations, the present distinction between
the two criteria makes an important first contribution to
research on context effects. This is because, first, the overlap
between the cognitive processes involved in the between- and
within-items effects is not perfect, and important theoreti-
cal distinctions remain such as the prediction of a negative
truth effect for disfluent items. Second, despite considerable
overlap, important empirical differences were observed. As
predicted, the between- and within-items effects were of dif-
ferent magnitude, they were affected by different moderators,
and a tendency toward a negative truth effect was found.
Dissociations. Support for the notion of different under-
lying processes comes from important empirical dissociations
between the within-items criterion and the between-items
criterion. Three main dissociations emerged: First, the between-
items effect was of greater magnitude than the within-items
effect. This observation is consistent with the above analysis
that judgments of nonrepeated (and therefore disfluent) items
are driven toward the “false” end of the scale in a heteroge-
neous context. Obviously, this line of reasoning implies that
when judgments for nonrepeated statements are compared
between the first and second sessions, we should observe a
negative effect, and this negative effect should account for the
difference in magnitude between the two criteria. We con-
ducted such an analysis on the eligible set of effect sizes (k =
29) and obtained the predicted negative effect of d = –.07
(with CIs ranging from –.14 to .01). Although this effect is
not significantly different from zero because of the smaller
number of eligible effect sizes, it is of comparable magnitude to
the difference between the between- and within-items effects
(see Table 1). We conclude that the negative truth effect
accounts for much, but not all, of the difference between the
between- and within-items effect sizes.
Second, increasing the delay between sessions increases
the within-items effect but not the between-items effect. This
suggests that, with increasing delay, the attribution of flu-
ency to the statement’s previous encounter (i.e., as familiarity)
is less likely to be successful, perhaps because of decreasing
source memory accuracy. Instead, the experienced fluency is
then attributed to a statement’s truth, in the sense of convergent
validity. Alternatively, a shorter delay might help participants
remember their first-session responses to the statements, and
a desire for behavioral consistency (i.e., a tendency to repeat
the first-session response) might then diminish the truth
effect. Other explanations are possible, but all explanations
have in common that delay moderates the within-items truth
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Dechêne et al. 253
effect via its influence on memory processes other than those
that support processing fluency. If delay affected fluency
directly, such an effect should also be reflected in the
between-items criterion. However, a moderation by delay
was not observed for the between-items effect. This suggests
that delay does not affect fluency directly and that the
between-items effect is less susceptible to explicit memory
processes such as those discussed above. Instead, the fact
that the between-items effect is independent of delay sug-
gests that it may come about mainly because of the differential
fluency experiences provided in a heterogeneous context.
This is consistent with a third difference between the
two criteria that emerged with regard to the moderating role
of verbatim versus gist repetition. The moderator did not
affect the within-items criterion; if, as suggested above, the
within-items effect relies more on explicit memory processes,
this could explain why in this case a repetition of a state-
ment’s gist—its conceptual meaning—is sufficient and why
an additional repetition of the exact wording is not benefi-
cial. The between-items criterion, in contrast, exhibited larger
effects for verbatim repetition than gist repetition, suggesting
that the underlying processes are low-level perceptual pro-
cesses typical of implicit memory effects (for an overview,
see Roediger, 1990).
In sum, moderation analyses yielded different patterns
for the between- and within-items effects. The findings are
consistent with the notion that there are different processes
underlying the two criteria: Although both an increase in
fluency because of repetition and an experience of a discrep-
ancy with a comparison standard play a role in both criteria,
the discrepancy experience in the heterogeneous context is
also boosted by the difference between relatively fluent (i.e.,
repeated) and relatively disfluent (i.e., nonrepeated) state-
ments at the time of judgment; this difference is fully reflected
only by the between-items criterion. As most of the studies
employed heterogeneous contexts, the truth effect in these
studies was influenced by a discrepancy between repeated
and nonrepeated statements, increasing the magnitude also
of within-items effect sizes computed for these studies. Future
research on the truth effect should carefully distinguish
between the effects of repetition itself and the effects of the
presence of nonrepeated, disfluent items at test. Moreover,
research should concentrate on both of the underlying cogni-
tive processes—the increase in fluency and the experience of
discrepancy—separately.
The Discrepancy-Attribution Hypothesis. The present
results suggest that the roles of discrepancy and of the compari-
son standard in fluency judgments require further attention.
According to the discrepancy-attribution account by Whittlesea
and Williams (1998, 2000, 2001a, 2001b), feelings of famil-
iarity result when the processing of a stimulus is experienced
as unexpectedly fluent (i.e., more fluent than expected on the
basis of a comparison standard), and this feeling is attributed to
a source in the past. Thus, if a surprisingly fluently processing
experience is interpreted as resulting from an event in the
past (i.e., a prior encounter with that stimulus), a feeling of
familiarity is elicited. Also well demonstrated is the influence
of processing fluency on other memory-based judgments such
as feelings of remembering (e.g., Jacoby & Whitehouse,
1989) and recall (e.g., Roediger & McDermott, 1995). Fur-
thermore, there is evidence that the discrepancy-attribution
account generalizes to recognition (Westerman, 2008).
Beyond memory-based judgments, the discrepancy-attribu-
tion account can explain the present findings on judgments
of truth as well as those of other fluency-based judgments
such as liking judgments (Alter & Oppenheimer, 2009;
Willems & Van der Linden, 2006). But despite the success of
the discrepancy-attribution account in explaining a wide
variety of judgment effects, little is known about the expe-
rience of discrepancy (and, for that matter, about the
attribution process). Investigations into these processes are
necessary to fill this void. The same is true for the comparison
standard that plays an important role in the discrepancy-
attribution hypothesis (cf. Whittlesea & Leboe, 2003). We
distinguished here between a comparison standard based on
internal expectancies (as in the homogeneous context) and
one generated on the fly from external stimuli (as in the het-
erogeneous context). The results suggests that there may be
substantial differences between the two types of comparison
standards; for instance, comparison standards based on internal
expectancies are likely to depend on individual characteris-
tics to a greater degree than standards based on external
stimuli. More research is needed that further investigates the
effects of this and other factors on the comparison standard
and, thereby, on the role of fluency on judgments.
Relation to Other Fluency-Based
Effects: Mere Exposure
The truth effect is one out of a class of fluency-based effects.
Another prominent example of this class is the mere exposure
effect (e.g., Bornstein, 1989; Bornstein & D’Agostino, 1992,
1994; Zajonc, 1968). Here, instead of judgments of truth, the
experience of fluency informs judgments of liking. Accord-
ing to the processing fluency/attribution model (Bornstein &
D’Agostino, 1992, 1994), prior exposure facilitates subse-
quent retrieval from memory, and this experience of ease is
interpreted as positive. As a consequence, repeated stimuli
are rated more favorably than new stimuli. Just as in the
case of the truth effect, corresponding results were obtained
using perceptual fluency manipulations: Highly visible stim-
uli are preferred over less visible stimuli (Reber et al., 1998;
Winkielman & Cacioppo, 2001).
According to the hedonic fluency hypothesis (Reber,
Schwarz, & Winkielman, 2004), easily processed stimuli are
generally preferred because they automatically elicit posi-
tive affect. However, it remains to be shown whether positive
affect is also involved in the emergence of the truth effect.
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254 Personality and Social Psychology Review 14(2)
On one hand, there is evidence for a link between positive
feelings and truth judgments (Garcia-Marques, Mackie,
Claypool, & Garcia-Marques, 2004). On the other hand, recent
evidence suggests that, when positivity is dissociated from
fluency, it is fluency, not positivity, that affects truth
(Unkelbach, Bayer, Alves, Koch, & Stahl, 2009); further-
more, it has been shown that the interpretation of fluency as
“true” is learned (Unkelbach, 2007) and involves controlled
cognitive processing, at least to some extent (Unkelbach &
Stahl, 2008). Therefore, it is not yet clear whether and how a
direct positive–true link exists and the extent to which this pos-
sible association is established automatically or by controlled
processing. Thus, the role of affect in the truth effect is not fully
understood, and future research on the truth effect and fluency
effects in general is needed to resolve this question.
The present results show that the truth effect and the mere
exposure effect share some moderating variables. Some of the
results obtained by Bornstein (1989) in a seminal meta-analysis
on the mere exposure effect correspond with our findings
on the truth effect: Both effects occur independently from
exposure duration (except for a tendency toward a smaller
truth effect for participant-paced presentation that is not easily
interpreted in terms of duration). Furthermore, both effects
are moderated by list type: They are found mainly under het-
erogeneous presentation conditions. The latter finding may
stimulate research on the similarity of contextual influences on
the fluency experience in the truth and mere exposure effects
(e.g., Dechêne et al., 2009; Willems & Van der Linden, 2006).
Somewhat in contrast to the mere exposure effect, we
found no clear influence of further repetitions on the truth
effect. (Note, however, that the effect of a second repetition
on the between-items criterion is consistent with the mere
exposure literature that also used this criterion.) The lack of a
clear effect may be a result of the small number of studies
available for that specific analysis. It may also be argued that
a judgment about truth is qualitatively different from a liking
judgment: Whereas a liking judgment is by definition based
on subjective experiences, a truth judgment can always be seen
before the background of an objective value. This may lead
to a ceiling effect in judgments because a statement cannot
be “truer” than “definitely true” by definition. In either case,
beyond noting important similarities, future research should
focus on qualitative differences between different types of
fluency-based judgments (for an overview of similarities,
see Alter & Oppenheimer, 2009).
Methodological Note
The present observations suggest some obvious methodologi-
cal recommendations. First, researchers interested in effects
of processing fluency should select the critical comparison—
between items or within items—in a principled manner, based
on theoretical considerations. Second, a principled choice of
judgment context and study design is probably even more
important: Researchers should be sensitive to the possible
contextual effects on the comparison standard that drives
fluency effects on judgments. More generally speaking, prefer-
ring a within-participants over a between-participants design
may not only affect statistical power but also affect the
context in which observations are made, which in turn may
substantially alter psychological processes involved. Sys-
tematic experimental investigations of this possibility are
highly desirable not only in the truth effect domain.
Practical Relevance
Effects of repetition have received high prominence in the
fields of advertising and persuasion (e.g., Batra & Ray, 1986;
Holden & Vanhuele, 1999; Nordhielm, 2002; Roggeveen &
Johar, 2002, 2007; Schumann, Petty, & Clemons, 1990). Here,
communication effectiveness is the focus of research on appli-
cations of repetition, and repetition effects are seen as based
on two factors or phases that influence message response
(Berlyne, 1970): The first is a “wear-in” phase of positive habit-
uation and increasingly positive responses. It may be followed
by a “wear-out” phase, characterized by too much repetition,
onset of tedium, and therefore decreasing message effective-
ness. The findings of the present analysis mainly contribute
to our understanding of the “wear-in” phase because data are
scarce for the effects of more than one repetition (although
there is a tendency that the truth effect wears off after one or
two repetitions).
An important factor for advertising effectiveness is the
consumers’ level of processing (e.g., Anand & Sternthal,
1990; Greenwald & Leavitt, 1984; Hawkins & Hoch, 1992).
This factor is thought to influence whether people encode
surface features of stimuli (i.e., low level of processing) or
whether they evaluate the semantic content of a stimulus (i.e.,
higher level of processing). The present analysis showed that
lower levels of processing reveal greater effects of repetition
on truth judgments; that is, a low level of processing at the
time of initial encoding leads to a more pronounced truth
effect. Thus, in case of an advertising strategy based on repeti-
tion, it is beneficial for advertisers when consumers engage
in shallower processing. Similar results have been obtained
for liking judgments on advertisements (Nordhielm, 2002).
Although the present meta-analysis did not obtain a sufficient
number of effect sizes to investigate this factor, source cred-
ibility may also be highly influential (e.g., Petty & Cacioppo,
1986). More research is needed to investigate the relative
roles and the interplay of levels of processing at initial encod-
ing versus at judgment.
A related point is the strategy of advertising variation (e.g.,
Schumann et al., 1990): This approach holds it to be benefi-
cial when an advertisement’s content varies over repetitions.
However, the present results suggest that an exact, verbatim
repetition is more effective in changing consumers’ belief in
a marketing claim. The present findings suggest that perhaps
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Dechêne et al. 255
a combination of repetition of core elements (i.e., to benefit
from implicit memory effects) and variation of peripheral
elements (i.e., to counter wear-out effects of tedium) may
be most effective. Finally, the finding that the truth effect is
largely independent of duration of stimulus exposure, delay,
and other variables leads to the conclusion that it is a reliable
phenomenon with relevant practical impact on advertising and
persuasion processes.
Conclusions
Two main conclusions can be drawn. First, the present review
has even more firmly established the existence of the truth
effect: Repeated presentation increases participants’ subjec-
tive judgments of a statement’s truth. The effect is of medium
size and occurs under a variety of conditions. Second, two
components of this effect can be distinguished, both theoreti-
cally and empirically: On a theoretical level, the psychological
processes underlying the truth effect differ between homoge-
neous and heterogeneous measurement contexts; empirically,
the within-items effect and the between-items effect were
of different magnitude, and they were differently affected by
moderating variables. These conclusions support an important
role of fluency (cf. Alter & Oppenheimer, 2009), and they
suggest that fluency effects are moderated by the context
in which judgments are performed. The next generation of
research on fluency effects on judgments should focus on such
contextual moderation.
Authors’ Note
Alice Dechêne and Christoph Stahl equally contributed to this work.
Declaration of Conflicting Interests
The authors declared no potential conflicts of interests with respect
to the authorship and/or publication of this article.
Financial Disclosure/Funding
The authors received no financial support for the research and/or
authorship of this article.
Notes
1. To the best of our knowledge, the zipper was invented in
Switzerland, and thus the statement, “The zipper was invented
in Norway,” is false.
2. This distinction between referential validity and convergent
validity is mirrored in remember versus know judgments regard-
ing specific memories (Gardiner & Richardson-Klavehn, 2000).
3. There is theoretical debate as to whether the process by which
fluency affects truth judgments is one of misattribution (e.g.,
Whittlesea & Williams, 1998) or whether it represents a valid
use of environmental cues (e.g., Hertwig, Herzog, Schooler, &
Reimer, 2008; Unkelbach, 2007). This distinction is not in the
focus of the present review, and we therefore remain neutral in
this debate.
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