A Source Like Any Other? Field and Survey Experiment Evidence on How Interest Groups Shape Public Opinion

Abstract

Interest groups increasingly communicate with the public, yet we know little about how effective they are in shaping opinions. Since interest groups differ from other public communicators, we propose a theory of interest group persuasion. Interest groups typically have a low public profile, and so most people are unlikely to have strong attitudes regarding them. Source-related predispositions, such as credibility assessments, are therefore less relevant in moderating effects of persuasive appeals by interest groups than those of high-profile communicators. We test this argument in multiple large-scale studies. A parallel survey and field experiment (N = 4,659) establishes the persuasive potential of low-profile interest groups in both controlled and realistic settings. An observational study (N = 700) shows that substantial portions of the public are unable to assess interest group credibility. A survey experiment (N = 8,245) demonstrates that credibility assessments moderate the impact of party but not interest group communication.

Full text

ORIGINAL ARTICLE
A Source Like Any Other? Field and Survey
Experiment Evidence on How Interest
Groups Shape Public Opinion
Andreas Jungherr
1
, Alexander Wuttke
2
, Matthias Mader
3
,&
Harald Schoen
2
1
Institute of Communication Studies, Friedrich Schiller University Jena, Ernst Abbe-Platz 8, D-07743 Jena
2
Department of Political Science, University of Mannheim, MZES, A5, 6, 68131 Mannheim
3
Department of Politics and Public Administration, University of Konstanz, Universita¨ tsstraße 10, D-78457
Konstanz
Interest groups increasingly communicate with the public, yet we know little about
how effective they are in shaping opinions. Since interest groups differ from other
public communicators, we propose a theory of interest group persuasion. Interest
groups typically have a low public profile, and so most people are unlikely to have
strong attitudes regarding them. Source-related predispositions, such as credibility
assessments, are therefore less relevant in moderating effects of persuasive appeals by
interest groups than those of high-profile communicators. We test this argument in
multiple large-scale studies. A parallel survey and field experiment (N ¼4,659) estab-
lishes the persuasive potential of low-profile interest groups in both controlled and re-
alistic settings. An observational study (N ¼700) shows that substantial portions of
the public are unable to assess interest group credibility. A survey experiment
(N ¼8,245) demonstrates that credibility assessments moderate the impact of party
but not interest group communication.
Keywords: Persuasion, Interest Groups, Political Communication, Source Credibility, Field
Experiments, Survey Experiments
doi: 10.1093/joc/jqab005
Governments, partisan actors, and international organizations routinely use com-
munication campaigns to shape public opinion. We increasingly see a new type of
actor, interest groups, running these campaigns. They typically have a low public
profile but often have considerable backroom influence (Du¨r & Mateo, 2016). In the
context of such “outside tactics” (Kollman, 1998), these actors try to persuade the
public as a way to generate additional pressure on decision makers to enact their
Corresponding author: Andreas Jungherr; e-mail: andreas.jungherr@gmail.com
Journal of Communication 71 (2021) 276–304 V
CThe Author(s) 2021. Published by Oxford University Press on behalf of
International Communication Association.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecom-
mons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the
original work is properly cited.
276
Journal of Communication ISSN 0021-9916
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preferred policies. For communication research, the question is whether established
theories allow us to evaluate the persuasive potential of these new communicators
correctly.
In this article, we argue that interest groups differ from established communica-
tors in an important way. Unlike communication by established communicators
such as political parties, interest groups typically have low public profiles. This raises
the possibility that two central tenets in general theories of persuasion do not hold
for interest group communication: namely, that source-related predispositions to-
ward these types of actors are available in people’s belief systems and that these pre-
dispositions moderate communication effects (Pornpitakpan, 2004;Self, 2009;
Wilson & Sherrell, 1993).
We develop this argument in several steps. First, we discuss the contemporary
role of interest groups as communicators with the public. Specifically, we identify
the strength of their public profile as a crucial characteristic in which interest groups
typically differ from sources that have conducted public communication campaigns
in the past. To give one example, in 2019, the National Rifle Association (NRA) was
mentioned 1,575 times in three leading U.S. newspapers, while the Republican and
the Democratic parties were mentioned 39,617 and 45,201 times, respectively.
1
Thus, the public profile of even the NRA—one of the most influential and visible in-
terest groups in American politics (Lacombe, 2019)—pales in comparison to that of
the two predominant political parties. Consequently, the public can be expected to
be much less familiar with the typical interest group than with actors continuously
at the center of public discourse.
We argue that this difference has important implications for the effects of per-
suasive attempts by these actors, especially with respect to the role predispositions
play in people’s reactions to their interventions. Indeed, the findings of three empiri-
cal studies reported below show that the persuasive effects of communicative inter-
ventions by low-profile sources are not moderated by prior attitudes about the
source, whereas they do so with respect to high-profile sources such as political
parties.
In the first study, we tested whether a communicative intervention by a German
business group with a low public profile could increase public support for an advo-
cated economic policy. We tested this in a parallel survey and field experiment with
three survey waves (N¼4,659). The relatively low-key intervention increased the sa-
lience of the policy addressed, persuaded recipients of the interest group’s position,
and increased the number of accessible supporting considerations. These effects
were modest in size and decayed over the course of a week. It is notable that we
found no evidence that recipients’ prior attitudes toward the interest group moder-
ated the persuasive appeal of the intervention.
In the second preregistered study (N¼700), we examined the availability of
credibility assessments for 10 environmental groups and 6 political parties in
Germany. We found that more respondents were unable to express credibility
assessments for the environmental groups than for the political parties. We also
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found that respondents who did express credibility assessments held them with less
certainty. Furthermore, perceived credibility of environmental groups corresponded
only weakly and not systematically with respondents’ party affiliations.
We used a high-powered, preregistered survey experiment (N¼8,245) to test di-
rectly whether a moderation of persuasive effects by credibility assessments is
weaker in interest group communication than political party communication. As
expected, we found that source credibility assessments did not moderate the persua-
sive appeal of an intervention by a low-profile environmental group in favor of a
program to increase energy efficiency. Similarly, for an environmental group with a
comparatively high public profile, there was at best weak evidence for a moderating
role of source credibility ratings. In contrast, prior attitudes did moderate persuasive
effects when we attributed the message to a political party. As theorized, those who
considered the party as a credible source on environmental issues changed their atti-
tudes in line with the party’s message, but those who found the party not credible
moved away from the advocated position, rendering the intervention counterpro-
ductive among these recipients.
We add to communication research by demonstrating the importance of exam-
ining closely the dynamics of persuasion by actors not traditionally in the focus of
communication scholars. Our findings indicate considerable differences in the de-
gree to which people hold and fall back on explicit credibility assessments for inter-
est groups and political parties. While interest groups and political parties both
seem able to shape public opinion, people appear to rely on prior source-related atti-
tudes when evaluating the messages sent by political parties but not interest groups.
By examining the effects of interest group communication and their dynamics, we
thus gain a deeper understanding of the conditions for predispositions to matter in
persuasion. In light of these findings, persuasion research needs to reflect that the
influence of source-related predispositions on the effects of communicative inter-
ventions varies for different types of actors.
Interest groups as communicators with the public
Interest groups and public communication campaigns
Interest groups are organizations that try to influence governments and the public
in line with the interests of their membership, which may be comprised of individu-
als or of other organizations. Interest groups are distinct from political parties in
that they do not seek offices by running candidates themselves but aim to influence
candidates and office holders (Berry & Wilcox, 2018, p. 5f.). While certain interest
groups have formed exclusive alliances with specific political parties in the past,
such ties have been weakening in many Western democracies in recent years, and
new types of interest groups have emerged that remain independent of traditional
political divisions. As a result, firm and exclusive ties between interest groups and
parties have become rare (see Allern, 2010).
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Beyond immediate links between interest groups and political parties, there may
be deeper links between political ideology and specific groups (Noel, 2013). This is
clearly the case for interest groups emerging along deep political cleavages, such as
the labor movement and its links to the political left. But even these strong historical
links have weakened over time (Kitschelt, 1994;Piazza, 2001). Clear ideological sort-
ing is even less pronounced for interest groups that have emerged only recently. For
example, the environmental movement can be linked to the political right as well as
the political left, depending on whether environmental groups present environmen-
talism as anti-technology and emphasize conservationist concerns or frame it as
anti-capitalist and anti-establishment (Dunlap et al., 2001;Gray, 1993;Nawrotzki,
2012;Neumayer, 2004;Pilbeam, 2003). Interest groups are thus best thought of as
distinct political actors who, in pursuit of specific issues, can have varying political
allegiances and who do not necessarily remain fixed in ideological space.
In face of weakened political alliances, interest groups increasingly employ
“outside tactics,” directly addressing the public (Kollman, 1998). While many pow-
erful interest groups used to concentrate on engaging politicians and decision mak-
ers directly (Du¨r & Mateo, 2016), they increasingly engage in extended public
communication campaigns. Recent examples include campaigns by MARQUES
(The Association of European Trade Mark Owners) in support of the “Anti-
Counterfeiting Trade Agreement” in 2012 (Du¨r & Mateo, 2014) and by the
Bundesverband der Deutschen Industrie in support of the Transatlantic Trade and
Investment Partnership (TTIP) in 2015–2016. Thus, there emerges a new set of
actors with considerable resources that engage in public communication campaigns.
It is one thing for interest groups attempting to persuade the public and another
to succeed at doing so (Arceneaux & Kolodny, 2009a, 2009b; Broockman & Kalla,
2016;Dewan, Humphreys, & Rubenson, 2014;Du¨r, 2019;Rogers & Middleton,
2015). While the literature on interest groups discusses the use of outside tactics in
issue campaigns, it focuses on portraying the repertoire of tactics employed and
does not theorize or test the effects of communication campaigns by interest groups
(e.g. Binderkrantz, 2005;2008;Binderkrantz & Krøyer, 2012;Du¨r & Mateo, 2016;
Hanegraaff et al., 2016;Kollman, 1998). The few studies that have tested communi-
cative interventions by interest groups indicate that they can act as effective commu-
nicators and persuade recipients (see Broockman & Kalla, 2016;Du¨r, 2019).
Persuasive effects come in many forms. Following Miller (1980), communicative
interventions can mean downright changing recipients’ minds on a topic (response-
changing effects) or just shaping the way they think about a topic, such as by raising
its salience or emphasizing the relevance of specific arguments in a debate (re-
sponse-shaping effects). But any persuasive intervention has to compete for atten-
tion in the noisy and competitive information environment of public discourse
(Druckman & Lupia, 2016). We must, therefore, test whether communicative inter-
ventions by interest groups have persuasive effects not only under optimal condi-
tions of exposure and reception but also under realistic, noisy conditions that are far
from optimal from a communicator’s perspective. In general, though, it seems
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plausible that interest groups, just as any other skilled communicator, have the po-
tential to persuade people:
H1: Communicative interventions by interest groups persuade recipients of
the position for which they argue, doing so by (a) increasing a topic’s salience,
(b) shifting attitudes toward the position, and/or (c) increasing the availability
of arguments raised.
By drawing on previous insights from communication and persuasion research,
we can go beyond this baseline hypothesis, however, and propose a more specific ar-
gument about the impact of interest group communication on public attitudes and
how it might differ from that of other communicators in the political arena, such as
political parties.
Low public profiles. The most important characteristic that sets interest groups
apart from other political actors is their typically low public profile, that is, their
presence in public discourse. The main political parties in a given country, for exam-
ple, are actors with high public profiles. They participate regularly in public dis-
course and take sides on the issues of the day. Most interest groups, such as business
or employers’ groups, have contrastingly much lower public profiles. Of course, the
public profiles of interest groups vary, and there are those that routinely participate
in public discourse (such as Greenpeace and the NRA, well-known public-facing in-
terest groups with long-established political positions). But even the public profiles
of relatively prominent interest groups are dwarfed in comparison with those of the
main political parties and their representatives.
2
For example, German national media mentioned the interest group Greenpeace
2,917 times in 2019, as compared with 85,375 and 80,615 mentions of the German
parties Sozialdemokratische Partei Deutschlands (SPD) and Christlich
Demokratische Union Deutschlands (CDU), respectively. This difference persists
once we examine the smaller—but nevertheless politically relevant—German parties
such as Freie Demokratische Partei (FDP) or Bu¨ndnis 90/Die Gru¨nen. These parties
had 26,741 and 23,242 mentions, respectively, in 2019. Thus, according to this mea-
sure, the public profile of the German interest group perhaps best known for its ag-
gressive outside tactics is lower than that of these small political parties by a factor
of 10.
This difference becomes even more apparent if we focus on the public profile of
business groups. For instance, the Arbeitgeberverband Gesamtmetall, a highly influ-
ential German employers’ group (Schroeder, 2017), was mentioned in German me-
dia 96 times during the same period.
3
These differences in public profile are no accident; they are rooted in the differ-
ent social functions of these actors. Political parties are “full-service” political com-
municators: they communicate continually with the public and take sides on issues
along the entire political spectrum. As a consequence, they are themselves the focus
of political coverage. In addition, people encounter political parties and their repre-
sentatives on various occasions in their daily lives, such as through interactions as a
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part of local politics. Interest groups, however, communicate selectively, focusing
only on issues that are important to them and appear only in the media if those
issues are featured. Furthermore, since most people do not follow politics closely,
only members of respective issue publics will encounter a given interest group di-
rectly or regularly. The public profile of interest groups is, hence, structurally deter-
mined and thus unlikely to change fundamentally.
Because the public profile of interest groups is typically low, it is not possible to
apply directly one of the core insights communication research has produced when
studying interest groups as public communicators. Specifically, we must question
the role of predispositions that moderate the effects of communication campaigns.
Can people be expected to link an interest group with a political ideology or party
reliably, or do they have prior attitudes toward the group that they rely on in reac-
tion to communicative interventions?
Do interest groups provide meaningful source cues? A key insight of commu-
nication and persuasion research is that recipients, in evaluating a message, consider
not only the content of the message itself—such as the quality of argument or
soundness of evidence—but also consider contextual cues (Chaiken & Ledgerwood,
2012;Chen & Chaiken, 1999). Contextual cues, by allowing recipients to assess the
credibility of a message, add to or detract from its persuasiveness.
In political communication, party cues are particularly important (Bullock,
2011,2020;Nicholson, 2011;Popkin, 1991). Studies show the strong moderating in-
fluence of party affiliation on the assessment of policy options and candidate evalua-
tions: Party messages influence supporters but are ineffective at changing the minds
of people “across the aisle”—or may even drive them further away (Arceneaux,
2008;Arceneaux & Kolodny, 2009a;Bartels, 2002;Berinsky, 2009;Bullock, 2011;
Kirkland & Coppock, 2018;Li & Wagner, 2020). Similarly, political partisanship has
been shown to influence the perception of content when presented by a politically
aligned or opposing information source, such as partisan news media or partisan so-
cial media users (Gunther et al., 2017;Lee et al., 2018;Reid, 2012). The importance
of partisanship cannot be generalized to all political communication, however, as it
hinges on certain conditions that are not necessarily met. Crucially, in settings
where research has found partisanship effects, the political affiliations of the sources
were clearly identifiable and unambiguous. Where communicators are less clearly
aligned along ideological or partisan divides, partisanship is bound to be less rele-
vant (Bullock, 2020, p. 138f).
In the case of interest group communication, it is doubtful that these conditions
are met. As described above, interest groups in contemporary Western democracies
are typically not linked exclusively or unambiguously with specific ideologies or po-
litical parties, and their public profile is, on average, quite low. While in some
Western democracies, such as the United States, extreme levels of political polariza-
tion lead to constellations in which some interest groups are linked unambiguously
with specific parties (Noel, 2013), such ties cannot be taken for granted. If we want
to understand the role of source-related predispositions in interest group
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communication, we must turn to specific source assessments and not general politi-
cal predispositions, which may not be related to a given interest group in a given
context.
Credibility assessment of the information source is the type of source evaluation
that seems to have received the most research attention (Hovland, Jannis, & Kelley,
1953;McGuire, 1969,1985;O’Keefe, 2016;Pornpitakpan, 2004;Self, 2009;Wilson
& Sherrell, 1993). A source’s credibility consists of judgments by people regarding
whether they should believe its communications (O’Keefe, 2016, p. 188f.). To make
such judgments, people are expected to use prior attitudes toward the source as well
as situational perceptions to assess its credibility. The positive evaluation that a
source is credible should increase the persuasiveness of a message. In turn, a nega-
tive credibility assessment of the same message should weaken its persuasive appeal
(Chaiken & Ledgerwood, 2012).
This line of reasoning is supported by a long series of empirical studies. Sources
recipients deem trustworthy and competent are more persuasive than those deemed
untrustworthy and incompetent (Gass & Seiter, 2018;McCroskey & Young, 1981).
Arguments presented by sources of high social repute, such as scientific publications
or government agencies, tend to be more persuasive than those by sources deemed
to be ill informed or predominantly self-interested, such as undergraduates or com-
mercial companies (Eastin, 2001;Gunther & Liebhart, 2006). This makes the credi-
bility assessment, the most likely candidate for moderating the persuasive appeal of
messages (Iyengar & Valentino, 2000;Lupia, 2002). It is an explicit assessment of
the source in question and is useful even in the absence of additional knowledge
about the sender—such as its links to political ideologies or parties.
But how convincing is it that credibility assessments matter for interest group
communication? This question has not been examined empirically; most studies
addressing source credibility focus on sources that are either well-known themselves
or belong to groups about which survey respondents hold pre-formed opinions
(such as the medical profession and scientific institutions). Studies on the role of
credibility assessment in cases where people have little information about the source
in question are missing from the literature (see, e.g., the list of studies in
Pornpitakpan, 2004 or Wilson & Sherrell, 1993).
Crucially, there are theoretical considerations that cast doubt on the notion that
credibility assessments play an important role in interest group communication.
Key among them is that the preconditions for the heuristic in question to become
relevant are not met (Chaiken & Ledgerwood, 2012). At the most basic level, if
recipients are unfamiliar with an interest group, they may simply not have a credi-
bility assessment to draw on. In such a situation, the particular heuristic of process-
ing the persuasive message is not available and cannot add to or detract from a
message’s persuasiveness. This is exactly what we expect to be the case when people
encounter political messages from interest groups, due to their low public profile.
And even if recipients are able to make a credibility assessment of an interest group
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on the fly,
4
it is unlikely to have the same impact on the processing of the message
as crystallized assessments.
This argument can be recast and generalized by drawing on the concept of atti-
tude certainty, that is, the “subjective sense of conviction or validity about one’s
attitude” (Gross, Holtz, & Miller, 1995, p. 215): The more certain recipients are
about their credibility assessments of the source, the more relevant those assess-
ments will be in evaluating the message. If credibility is assessed to be uncertain, this
particular heuristic will play less of a role in adding or detracting from the message’s
persuasive appeal.
Finally, it seems unlikely that individuals can rely on partisan affiliations when
constructing credibility assessments of an interest group. As noted above, this is be-
cause most interest groups do not exhibit clear links to a single political party or po-
litical ideology.
In sum, neither sender-specific credibility assessments nor party affiliation—or
similar general political predispositions—are likely to matter much for processing
persuasive messages of interest groups. These considerations lead to the following
hypotheses:
H2a: Respondents are less likely to express credibility assessments for interest
groups than for political parties.
H2b: Respondents express less certainty about credibility assessments of inter-
est groups than about credibility assessments of political parties.
H2c: Credibility assessments of interest groups are not linked systematically to
party identifications.
H3: Credibility assessments will influence the persuasive effects of party com-
munication stronger than interest group communication.
While these hypotheses treat interest groups as a homogenous category, we have
pointed out above that some of these groups have higher public profiles than others.
The proposed differences between parties and interest groups should be particularly
pronounced when comparing political parties with the large number of interest
groups with low public profiles. It is less clear what to expect when comparing polit-
ical parties to the handful of relatively prominent interest groups with high public
profiles. Two scenarios seem possible. One is that the public profile of interest
groups such as Greenpeace or the NRA could be sufficiently high for people to form
meaningful credibility assessments (i.e. assessments held with certainty), which
might in turn serve as available heuristics. Accordingly, in the case of interest groups
with high public profiles, credibility assessments might add to or detract from per-
suasive appeals in the same way as they do for political parties. But given the vast
difference between the public profiles of even the most visible interest groups and
the least visible major parties, as shown above, another outcome is just as likely: it
may be that even interest groups with a comparatively high public profile do not
achieve the degree of visibility necessary for the average citizen to develop crystal-
lized credibility assessments. If true, we should expect credibility assessments of
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interest groups with high public profiles to have little or no impact on the processing
of their messages. Consequently, we consider it an open question whether the pat-
terns expected in H2a, H2b, H2c, and H3 also hold for the small set of interest
groups with relatively high public profiles.
Study 1
Data and methods
We used a combined field and survey experiment design to examine the effects of a
communicative intervention by an interest group with a comparatively low public
profile in a competitive and noisy communication environment. In order to provide
a realistic context for our experiment, we collaborated with the German business
group Arbeitgeberverband Gesamtmetall (Federation of German Employers’
Associations in the Metal and Electrical Engineering Industries), which represents
the interests of German companies in those two sectors. Given the importance of
these industries to the national economy, Gesamtmetall can be considered one of
the most politically influential employers’ groups in Germany (Schroeder, 2017).
However, its influence does not translate into prominence in public discourse.
5
In collaboration with the group, we developed an information mailing reflecting
its actual policy position. The mailing presented three arguments in support of the
Transatlantic Trade and Investment Partnership (Jungherr, Mader, Schoen, &
Wuttke, 2018). In addition, the letter included various statements in favor of the rat-
ification of the agreement. It was sent in an envelope clearly identifying the sender
and its support for TTIP (see Appendix S2 for treatments).
The experiment was conducted in three waves between 21 April and 22 June
2016 with members of a large German online panel Payback, and was executed on
our behalf by the survey company Infratest dimap. To ensure correspondence be-
tween the respondents and the German online population, we used quotas blocking
access to the survey for respondents with specific demographic characteristics once
their share had reached levels comparable with their share of the German online
population. The realized sample size was N¼7,826. We randomly assigned partici-
pants into three groups. The field experiment group (N¼2,606) received the infor-
mation letter by mail, the survey experiment group (N¼2,609) was exposed to the
mailing embedded in the questionnaire, and the control group (N¼2,611) received
no treatment (see Appendices S3–S5 for details).
Wave 1 of the survey (N¼7,826), which ran before treatment administration
(21 April–11 May 2016), measured attitudes toward TTIP, demographic character-
istics, and predispositions expected to moderate the effects of the planned treatment.
Nineteen days after the close of wave 1, the information mailing was sent to the field
experiment group (30 May). In wave 2 (N¼6,171), which began six days later (6
June–13 June), respondents in the survey experiment group were shown the same
letter on screen that respondents in the field experiment group had received by
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mail. To measure effect decay, we conducted a final survey wave one week later
(N¼4,659) (20 June–22 June). Waves 2 and 3 included items to measure TTIP atti-
tudes, considerations about the agreement, and subjective attitude certainty (see
Appendix S6 for the questionnaire; see Appendix S7 for indicators). For the analyses
presented in the article, we rely only on answers by respondents who participated in
all three waves and reported an attitude toward TTIP in wave 1 (N¼4,659).
6
The comparison of the treatment’s effects under field and survey conditions
allows complementary insights into its effects on respondents. Under field condi-
tions, we can assess the persuasive strength of interest group communication over
time in competitive and noisy communication environments. The survey condition
promises a detailed view of the strength of persuasive effects under close-to-ideal
measurement conditions, given controlled exposure and measurement directly after
exposure. This allows the identification of small or heterogeneous effect patterns.
Because treatment compliance and time of exposure are known, it is also much eas-
ier to calculate a realistic decay rate of persuasive effects. We thus capitalize on the
strengths of both experimental modes while offsetting their weaknesses (Harrison &
List, 2004), whereas previous studies focused on the comparability and relative
advantages of each experimental mode (Barabas & Jerit, 2010;Findley, Laney,
Nielson, & Sharman, 2017;Jerit, Barabas, & Clifford, 2013).
Results
To address the first hypothesis, we estimated the main treatment effects in a series
of Ordinary Least Squares (OLS) regressions. For each of the three panel survey
waves, we regressed the three dependent variables (TTIP SALIENCE, TTIP
ATTITUDE, and NUMBER OF PRO-TTIP ARGUMENTS) on dummy variables
indicating a respondent’s treatment assignment and, to increase efficiency, a pre-
treatment measure of the dependent variable (Gerber & Green, 2012).
7
Figures 1, 2,
and 3 show the results. Specifically, we report differences in predicted means of the
dependent variables between the control, field, and survey groups, respectively.
Coefficients in wave 1 show that the experiment groups did not differ significantly
before the treatments were administered.
8
In comparing treatment effects in the field and the survey conditions, note that
these experiments followed somewhat different logics. In the survey condition, treat-
ment compliance was ensured by design because respondents were exposed to the
treatment as part of the survey itself.
9
In the field condition, we look at people we
intended to treat with the mailing. In the unobtrusive conditions of a field experi-
ment, however, it is likely for a variety of reasons that some participants assigned to
receive the treatment did not read the letter. Comparing the effects in the field and
the survey conditions thus means comparing treatment effects in two different
groups: one in which all subjects saw the information letter at least briefly (survey)
and a group in which only a fraction did (field). In addition, the effect measured in
wave 2 has likely already decayed in the field condition due to a time gap of
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unknown length between exposure and measurement, whereas measurement imme-
diately followed treatment exposure in the survey condition. We should, therefore,
examine the survey condition to assess the treatment’s effect strength under ideal
exposure and measurement conditions. To gain an impression of how the treatment
fares under realistic exposure conditions, we should turn to the field condition while
considering the caveats described.
According to Hypothesis 1, the treatment should increase the salience of TTIP,
support for TTIP, and the number of pro-TTIP arguments of which respondents
are aware. As Figures 1, 2, and 3 report, the findings from both experimental modes
support this, but to different degrees. Figure 1 shows that the treatment had notice-
able and somewhat durable effects on respondents in the survey experiment condi-
tion. Respondents who had read the letter embedded in the survey considered the
TTIP issue to be slightly more important than respondents in the control group
(treatment effect on the dependent variable scaled from 0–1: 0.049 [95% CI 0.035–
0.062], Cohen’s d: 0.23). The effect is still visible at about half its original size when
attitudes were measured a week later in wave 3 (0.029 [0.016–0.042]).
10
In the field
condition, there is no comparable effect dynamic—although TTIP salience is higher
in the field group than in the control group both in wave 2 (treatment effect: 0.013
Figure 1 Treatment effects on TTIP salience. Notes: The figure reports differences between
the control group and the treatment groups; bars indicate 95%confidence intervals. The
results are based on linear regressions of TTIP salience on dummy variables indicating
group membership. The range of the salience measure is 0–1. To increase the efficiency of
the treatment estimate, a pretreatment measure of the outcome variable from wave 1 is in-
cluded as covariate in the regression.
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[0.000–0.0268], Cohen’s d: 0.03) and wave 3 (0.019 [0.005–0.031]), the numerical
effects are small and somewhat unreliable.
The results for TTIP support, the second dependent variable, are more consis-
tent across experimental modes. Figure 2 shows that in wave 2, respondents
assigned to read the letter showed significantly higher support for TTIP than
respondents in the control group. As expected, the effect is again substantially larger
in the survey (treatment effect: 0.119 [0.104–0.133], Cohen’s d: 0.43) than in the
field condition (0.031 [0.017–0.045], Cohen’s d: 0.12). Both effects decay but remain
statistically significant in wave 3 (effect in survey: 0.050 [0.037–0.064], effect in field:
0.015 [0.001–0.029]).
Recent developments in experimental research have raised awareness in the field
that coefficients and p-values do not necessarily indicate the practical relevance of
effects (Calin-Jageman & Cumming, 2019;Flora, 2020;Pek & Flora, 2018). Yet, this
is important in assessing whether interest groups can influence public opinion to a
meaningful degree.
Since the literature has not converged on a universal assessment of effect sizes,
suggesting instead a number of different approaches (Lakens, 2013), we apply three
intuitive approaches to assess effect sizes on TTIP support—which may arguably be
.005 .012 .031 .119 .015 .051
Mean:
Control Group
with 95% CI
+0.05
+0.10
+0.15
Wave 1
Mean of
Control Group:
0.44
Wave 2
Mean of
Control Group:
0.41
Wave 3
Mean of
Control Group:
0.43
Field
Survey
Figure 2 Treatment effects on TTIP attitude. Notes: The figure reports differences between
the control group and the treatment groups; bars indicate 95%confidence intervals. The
results are based on linear regressions of TTIP attitude on dummy variables indicating group
membership. The range of the attitude measure is 0–1. To increase the efficiency of the
treatment estimate, a pretreatment measure of the outcome variable from wave 1 is included
as covariate in the regression.
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considered the most important dependent variable in our study. We begin by look-
ing at the percentage of overlap in the distributions of the outcome variable in the
control and the experimental groups (Calin-Jageman, 2018). In the survey experi-
ment, we observe an overlap of 84% in the distributions of TTIP attitudes between
the control and the experimental group in wave 2. This distribution translates into a
63% probability that a member of the survey treatment group supported TTIP more
strongly than a person from the control group, indicating a substantial treatment ef-
fect. In comparison, the effect in the field condition is much smaller: the attitude
distributions of the field and the control groups overlap by 95% (wave 2), which
means that the probability of a randomly chosen individual from the field group
having a more favorable opinion on TTIP than a randomly chosen individual from
the control group is only 54% (i.e., only slightly higher than chance).
Dichotomizing the outcome variable provides another useful metric to get a bet-
ter understanding of an effect size’s substantive significance. In wave 2, 32% of the
respondents in the control group showed TTIP attitude scores larger than 0.5 (i.e.,
had positive attitudes toward TTIP). In the survey group, the corresponding per-
centage is 53%, suggesting that the survey treatment transformed aggregate opinion
Figure 3 Treatment effects on number of pro-TTIP considerations. Notes: The figure reports
differences between the control group and the treatment groups; bars indicate 95%confi-
dence intervals. The results are based on linear regressions of the number of pro-TTIP argu-
ments on dummy variables indicating group membership. One unit on the considerations
measure represents one pro-TTIP consideration mentioned. To increase the efficiency of the
treatment estimate, a pretreatment measure of the outcome variable from wave 1 is included
as covariate in the regression.
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from clear opposition to slim support. In the field experiment setting, the share of
TTIP supporters was 38% in wave 2, indicating that mailing the letter resulted in a
difference of a mere 6 percentage points compared to the control.
Categorizing respondents into supporters or opponents of TTIP further allows
us to estimate the practical significance of the persuasion effort by the interest group
from a cost–benefit perspective. The “numbers needed for change” effect size
(Gruijters & Peters, 2019) illustrates that treating seven participants with the survey
experiment stimulus would persuade one additional participant that the free trade
agreement merits support, compared to the control group. In the field, the interest
group can expect to generate one additional supporter for every 23 letters it sends
out.
As noted above, we should consider that not all participants we assigned to the
field condition actually received and processed the treatment. Indeed, only 51% of
these respondents reported to have read the letter. Naturally, the treatment’s effect
on attitude change will be larger among compliers than among the entire group of
individuals assigned to the field treatment. Although self-reported recalls of treat-
ment compliance are likely subject to measurement bias, they allow us to estimate,
at least coarsely, the effects on the treated using two-stage least squares (Gerber &
Green 2012). Accordingly, the effect on an individual who reported to have opened
and read the letter was 0.06 (p<.001) in wave 2 (as opposed to .03 when consider-
ing all members of the treatment group). Hence, in a natural environment, the inter-
est group’s letter had a small but noticeable effect on those individuals who reported
to have read it. In practical terms, this effect means that the interest group would
generate one additional supporter of TTIP for every 13 people who read the letter.
In combination, all three assessments show that the strength of the treatment ef-
fect on changing opinions was limited but clearly identifiable and potentially practi-
cally relevant during the course of a public information campaign.
Moving on, the treatment’s effect on the number of accessible considerations in
favor of TTIP resembles the effects on TTIP salience (see Figure 3). In wave 2,
respondents in the survey experiment could recall, on average, 0.2 (95% CI 0.145–
0.255, Cohen’s d: 0.23) additional arguments in favor of TTIP. A smaller but signifi-
cant effect was also visible in the field experiment condition (0.066 [0.010–0.121],
Cohen’s d: 0.08). This initial effect decayed between waves 2 and 3 to roughly half
its size, and remained statistically significant only among respondents in the survey
condition (0.091 [0.040–0.142]).
11
Effects were substantial in the survey experiment condition and small but not
negligible in the field experiment condition with respect to all three dependent vari-
ables in wave 2. In wave 3, these effects had substantially decayed. In sum, we find
support for Hypothesis 1. These results are consistent with the view that interest
group interventions have an effect on public opinion, but suggest that the success of
a single intervention (at least in the form of an information letter) is short lived.
To gain a first intuition of whether persuasive appeals by interest groups with
low public profiles are moderated by recipients’ prior attitudes toward a source, we
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re-estimated the regression models reported above, adding interaction terms be-
tween the treatment dummies and the respondents’ prior attitudes toward the
sender. Specifically, as a moderating variable we rely on attitudes toward the role of
employers’ groups in politics in general.
12
Table 1
13
shows little evidence of any substantial interaction effect of prior atti-
tudes toward the employers’ group influence in five of the six analyses in this setup.
The one deviant finding is that attitudes toward employers’ groups seemingly mod-
erated the number of pro-TTIP arguments mentioned by respondents in the field
condition (p¼.018). This effect did not replicate in the survey condition (p¼.270),
however, and disappeared once we controlled for multiple comparisons
(Bonferroni-corrected p-value of interaction with field-treatment: .108), casting
doubt on the notion that prior attitudes played a systematic role in moderating the
effects of the interest group communication.
14
In sum, the findings are in line with our argument about the persuasive appeal
of interest groups with low public salience. However, we have not yet presented sys-
tematic evidence to support our claim that interest groups have a relatively low pub-
lic profile, nor have we directly tested the effects of messages from different senders.
We turn to these questions next.
Study 2
Data and methods
We now assess our claim that interest groups have a relatively low public profile
(Hypotheses 2a–c).
15
To assess the public profiles of political actors, we conducted a
Table 1 Conditionality of Treatments Effects Depending on Prior Attitudes on
Employers’ Group Influence (study 1: wave 2)
Salience Attitude No. of pro-TTIP arguments
Field Survey Field Survey Field Survey
0.00
(0.03)
–0.01
(0.03)
0.04
(0.03)
0.03
(0.03)
0.25
*
(0.11)
0.11
(0.11)
Notes: Reported are interaction effects between the moderator and the experimental
condition mentioned in the respective column headers. Results are based on linear
regressions and standard errors are reported in parentheses. Dependent variables were
measured in wave 2, while moderators were measured in wave 1. Full regression tables
are provided in Appendix S10.
*p<.05.
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survey to measure the availability of credibility assessments and associated attitude
certainty of 10 environmental groups (registered with the German federal govern-
ment) and 6 political parties. We queried how credible survey respondents thought
a given group or party was when communicating on environmental issues (see
Appendix S15 for the questionnaire; see Appendix S16 for indicators). Interviews
with 700 members of the German online panel Respondi were conducted between
31 March and 6 April 2020. To ensure that this sample corresponded to the German
online population, we used quotas blocking access to the survey for respondents
with specific demographic characteristics once their share had reached levels com-
parable with their share of the target population.
To identify a set of interest groups with comparatively high and low public pro-
files, we began with a list of all environmental groups registered with the federal
government that are membership organizations with a national focus.
16
To this ini-
tial set, we added groups based on communication with a professional working in
environmental advocacy. This left us with 108 environmental groups, for whom we
infer public profiles based on their mentions in German media in 2019.
17
For our
set of 10 environmental groups, we selected the 5 with the highest number of media
mentions during 2019 and added another 5 that were randomly selected. To identify
a set of political parties, we relied on representation in the German federal parlia-
ment as the selection criterion. Thus, we are able to test the availability of credibility
assessments and the certainty with which they are held for five environmental
groups with comparatively high profiles, five with comparatively low profiles, and
six political parties.
Results
The distributions of credibility assessments support Hypothesis 2a, which states that
respondents are less likely to express credibility assessments (be they positive or
negative) for interest groups than for political parties (see Table 2). Roughly 9 of 10
respondents were ready to provide credibility assessments of political parties.
Greenpeace was the only interest group to reach a similar level. For all other interest
groups, respondents indicated much more frequently that they were unable to assess
the groups’ credibility. Our preregistered, formal test also shows that the aggregated
index of unavailable credibility assessments of interest groups (mean: 0.50, 95% CI
0.47–0.53) was much higher than credibility assessments of political parties (mean:
0.10, 95% CI 0.08–0.12). In short, considerably fewer respondents could form credi-
bility assessments for interest groups than for political parties. At the same time, the
higher variation in available credibility assessments of interest groups compared to
political parties also encourages the above-mentioned differentiation between low-
profile and (relatively) high-profile groups.
Examining the certainty with which credibility assessments were held among the
subset of respondents that voiced credibility assessments for a particular group, the
findings again conformed with our expectation: respondents were less certain about
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credibility assessments of interest groups than about credibility assessments of polit-
ical parties (Hypothesis 2b). The formal, preregistered test shows that an aggregated
index of certainty of credibility assessments regarding interest groups (mean: 0.52
[0.50–0.54]) was considerably lower than certainty regarding political parties (mean:
Table 2 Characteristics of Interest Groups and Parties (study 2)
Group Media men-
tions, 2019
Credibility
assessment
available
(in %)
Explained
variance by party
identification
No. of
observations
Interest group, high profile
Greenpeace 11,167 88 0.09 535
Deutsche Umwelthilfe 5,660 75 0.06 449
Naturschutzbund
Deutschland (NABU)
1,909 79 0.07 476
Bund fu¨r Umwelt und
Naturschutz Deutschland
(BUND)
1,405 79 0.08 478
Germanwatch 1,212 47 0.01 280
Interest group, low profile
NaturFreunde
Deutschlands
135 52 0.05 313
Deutscher
Naturschutzring
128 53 0.04 321
Bundesdeutscher
Arbeitskreis fu¨r
Umweltbewusstes
Management (B.A.U.M.)
16 49 0.02 300
MUNA e. V. Mensch,
Umwelt-, Natur- und
Artenschutz
2 45 0.02 276
Naturschutzforum
Deutschland e. V.
0 50 0.04 302
Party
CDU/CSU – 91 0.24 555
SPD – 90 0.27 548
AfD – 89 0.37 542
FDP – 88 0.12 537
Die LINKE – 88 0.25 537
Bu¨ndnis 90/Die Gru¨nen – 92 0.28 558
Notes: The columns “Explained variance by party identification” and “No. of observa-
tions” report summary statistics of linear regression analyses of the organizations’ per-
ceived credibility with respect to environmental issues as the dependent variables
regressed on the respondent’s identification with a political party (measured in six bi-
nary variables).
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0.60 [0.57–0.62]). Overall, familiarity with political parties is widespread among
respondents, but only a fraction knows interest groups well enough to express credi-
bility assessments and, even when they do, they express these assessments with con-
siderable uncertainty.
18
Finally, credibility assessments are only weakly related to party affiliations.
Column 4 in Table 2 reports how well the respondents’ self-reported attachment to
German political parties (measured in six dummy variables) explains variance in
credibility assessments of interest groups and political parties. We see that party
identification has exceptionally low explanatory power R
2
to predict credibility
assessments of interest groups. As expected, party identification is more closely re-
lated to how credible parties are perceived to be on a specific political issue but, in-
terestingly, the association is far from perfect. Thus, in accordance with our
characterization of interest groups, respondents’ credibility assessments do not clus-
ter along partisan lines.
19
In sum, the findings support our expectations. The lower public profile of inter-
est groups is reflected in a higher absence of source credibility assessments in the
general public. Those who do report such assessments tend to be less certain about
the assessment of interest groups than of political parties, and credibility assess-
ments of interest groups in general tend to be weakly connected with party affilia-
tions. All this bolsters the expectation that source-related predispositions should
play a smaller role in moderating interest group communication compared to com-
municators with high public profiles. This is true in the basic sense that predisposi-
tions that a person does not hold cannot influence their attitudes or behavior.
Furthermore, it stands to reason that attitudes that do exist but are held with lower
certainty may not influence the processing of a given message. We turn to this ex-
pectation next.
Study 3
Data and methods
We designed this study to contrast the role of credibility assessments in processing
communicative interventions from different types of political actors—namely, polit-
ical parties and interest groups with high and low public profiles (Hypothesis 3).
20
We conducted a large-scale survey experiment among members of the German on-
line panel Respondi between 28 April and 13 May 2020 (N¼8,245). The large sam-
ple size was deliberate to allow for reliable identification of effect moderation and is
based on the results of a preregistered power analysis (see Appendix S19). To ensure
correspondence with the German online population, we used quotas blocking access
to the survey for respondents with specific demographic characteristics once their
share had reached levels comparable with their share of the German online
population.
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We designed a treatment in support of an environmental policy targeted at re-
ducing energy waste resulting from inefficient thermal isolation in buildings.
Respondents assigned to different treatment groups were shown the treatment with-
out source attribution (N¼1,630), attribution to a high-profile interest group
(N¼1,688), a low-profile interest group (N¼1,587), and a political party
(N¼1,674). A control group was exposed to no treatment (N¼1,166).
21
In selecting interest groups for our treatments, we built on findings from our
previous study, in which we tested the availability of credibility assessments for dif-
ferent interest groups. Based on these results, we chose Greenpeace, the group with
the highest familiarity among respondents, to stand in as an example for a high-
profile group, and we chose Deutscher Naturschutzring, one of those with lower fa-
miliarity among our respondents, as an example of a group with a low public profile.
For the party source, we selected the German Christian Democrats (CDU/CSU),
which is the majority partner in Germany’s governing coalition and thus has over-
seen deep reforms as part of Germany’s turn toward renewable energy. At the same
time, it is not a party traditionally associated with pro-environment policies.
Results
While our goal was to test the moderating role of credibility assessments for persua-
sion effects, we begin with a discussion of the average effects of the persuasive inter-
vention. We did not find a consistent positive effect of our treatment (means with
95% CIs control: 0.447 [0.440–0.456]; no source: 0.441 [0.432–0.450]; low profile
IG: 0.429 [0.420–0.438]; high profile IG: 0.440 [0.431–0.448]; party: 0.430 [0.421–
0.438]) (see Appendices S20.2 and S20.3 for treatment materials). This deviates
from pre-test results, in which a plain text-version of the treatment had elicited
small but significant positive effects (means with 95% CIs: control: 0.482 [0.463–
0.501]; no source: 0.519 [0.499–0.538]) (see Appendix S20.1 for treatment
materials).
Pre-test and main test, therefore, leave us with contradictory evidence regarding
Hypothesis 1, with only the pre-test weakly supporting H1. This could be due to a
change in treatment design. The main test treatment relied more heavily on graphics
than the pre-test treatment and may have been less persuasive than intended. In
combination with the evidence presented in Study 1, this apparently shows that the
persuasive appeal of communicative treatments by interest groups cannot be taken
for granted but also depends on content and context.
22
Our interest here, though, does not concern the main effects of the treatment
but the role of perceived source credibility in moderating the effects of political
communication. To examine the role of source credibility, we tested whether the
level of attitude change in subgroups with positive and negative prior credibility
assessments of selected sources differed when the same message was attributed to a
political party (CDU/CSU), an interest group with a comparatively high public
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profile (Greenpeace), and an interest group with a comparatively low public profile
(Deutscher Naturschutzring).
The data support Hypothesis 3. Given the same persuasive treatment, respond-
ents relied on prior credibility assessments when the source was a political party but
not when it was an interest group.
23
As Figure 4 shows, we found no significant
moderating effects of source credibility assessments either for the interest group
with the highest public profile (Greenpeace) or for an interest group with a compar-
atively low public profile (Deutscher Naturschutzring). In contrast, among those
who considered the party (CDU/CSU) a credible communicator on environmental
issues, respondents who received the treatment message from CSU/CSU (N¼303)
changed their position on the issue in the party’s direction by 0.039 (95% CI 0.011–
0.068; Cohen’s d: 0.23) points on a scale from 0 to 1, compared to respondents with
favorable attitudes toward CDU/CSU who received the identical message without
any sender cues (N¼317). Among those who considered CDU/CSU not to be a
credible communicator on environmental issues, the treatment even made respond-
ents less supportive of the position advocated by the CDU/CSU: among respondents
in the party treatment group with unfavorable prior attitudes toward CDU/CSU
(N¼1,327), support for the issue dropped by –0.022 scale points (95% CI –0.036 to
–0.008; Cohen’s d: –0.12) compared to the no source group (N¼1,231). The result
of this preregistered analysis of the difference between treatment effects across
Figure 4 Differential treatment effects conditional on type of communicator. Notes: The fig-
ure shows coefficients from linear regressions that denote treatment effects within subgroups
of individuals who reported high or low prior credibility assessments (split at scale mid-
point) toward the respective sender of the message.
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subgroups is statistically significant (p<.001), lending support to the proposition
that credibility assessments moderate the persuasiveness of communicative inter-
ventions by political parties.
In sum, the findings of Study 3 are in line with the broader argument that pre-
dispositions such as credibility assessments play a minor role in the effects interest
group messages have on public opinion because people are less familiar with these
actors. This sets interest group communication apart from party communication,
where predispositions matter more because people can fall back on previously held
assessments of these high-profile sources.
Discussion and conclusion
As interest groups increasingly run communication campaigns to shape public
opinion, understanding their role as public communicators becomes important.
This article takes a significant step in that direction. It contributes to the emerging
literature on interest groups as communicators with the public (Broockman &
Kalla, 2016;Du¨r 2019) and advances political communication research in general by
adding to our understanding of the characteristics and effect patterns associated
with a new type of communicator (Arceneaux & Kolodny, 2009a,2009b;Dewan
et al., 2014;Rogers & Middleton, 2015). We have shown that interest groups, like
other skilled communicators, have the potential to shape public opinion (Study 1,
Study 3 pre-test). That being said, communicative interventions by interest groups
are not always successful in persuading respondents (Study 3 main test). We have
also presented evidence that interest groups typically have a low public profile, and
that this characteristic has implications for how these actors are perceived and how
their messages are received by the public. People make credibility assessments of in-
terest groups less frequently than they assess political parties, and when they do,
they are less certain (Study 2). Correspondingly, we found that credibility assess-
ments do not moderate effects of communicative interventions by interest groups as
they do for those by political parties (Study 3).
These findings have important implications for the impact of interest group in-
formation campaigns. As many recipients have no or inconsequential prior attitudes
toward these low-profile sources, interest groups may neither hope for a boost in
nor need fear a penalty against persuasiveness from these attitudes. In this respect,
their interventions appear to differ from those of actors with higher public profiles,
such as political parties and government representatives. The absence of credibility
moderation does not imply, of course, that interest groups are generally more effec-
tive communicators than political parties. However, whereas the persuasiveness of
party communication is confined to segments of the population that are open to
messages from these parties and may even have detrimental effects on others, many
interest groups have the potential to address the entire public successfully.
We showed that recipients draw little information from the source cues of low-
profile senders. Therefore, the impact of a persuasive appeal depends on the
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strength of the message itself. This finding contributes to theorizing on the role of
source credibility in persuasion more generally. Prior research on the topic typically
assumes (implicitly) that people hold meaningful credibility assessments regarding
the sender in question (see, e.g., the studies listed by Pornpitakpan, 2004;Wilson &
Sherrell, 1993). We have argued, in contrast, that the effects of source credibility
assessments depend on the availability and certainty of attitudes toward specific
actors, and we have shown that these vary. If people do not hold meaningful credi-
bility assessments of a sender, these assessments cannot influence the processing of
the message. Our study thus also contributes to the important body of research ex-
amining the role of source-related predispositions in persuasion (O’Keefe, 2015;
Stiff & Mongeau, 2016).
Naturally, our analysis has some limitations, which means that our conclusions
are to some extent preliminary and call for additional research. To start, the evi-
dence presented here stems from only one national context, so we cannot say for
certain whether the findings—and implications—hold in other contexts. At a very
general level, the German communicative context is similar to that of other Western
democracies. Zooming in, however, one could expect select interest groups in politi-
cally more polarized contexts—such as the NRA in the United States—to have ex-
clusive links to political parties, to be linked unambiguously with political
ideologies, or even to have public profiles comparable to those of political parties,
and hence also to have to contend with effect moderation. This would be consistent
with our general theoretical argument, which hinges on the strength of the public
profile communicators have. Accordingly, key tasks for future research remain to
identify the threshold at which the public profile of an interest group (or any other
public communicator) is sufficiently high to trigger source-based effect moderation
and to analyze the effects of different constellations in the alignment of interest
groups with political parties and interest groups.
Similarly, public profiles of interest groups might change over time. Constant
campaign activity could increase the public profiles of interest groups so that people
develop meaningful credibility assessments, and consequently trigger the modera-
tion of persuasive effects. We expect such evolutions to be rare, however, given the
different functions interest groups and political parties serve in modern societies.
Interest groups tend to communicate on only one or a few issues they care about,
while political parties communicate continually on multiple issues on the agenda.
Even factoring out the nontrivial question of financing prolonged communication
campaigns, for interest groups to develop public profiles comparable to that of polit-
ical parties would require either that they begin to communicate on the full spec-
trum of issues on the agenda or that the agenda be reduced, for long periods, to the
few issues about which they care. That being said, the dynamics of the public profile
of interest groups and their implications for source credibility assessments at the
public level is an important topic for future research.
While we covered two different issue domains in our empirical analysis, we did
not study systematically how different features of a given issue domain might
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strengthen or weaken source-based moderation effects. For example, topics with
high ego-involvement might motivate recipients to engage with the content of a
message—irrespective of prior attitudes they may have toward the sender.
Conversely, with respect to highly politicized topics, people may act on even vague
suspicions about the political alignment of a low-profile sender. Future research
should explore these possibilities systematically in order to explore the generalizabil-
ity of our findings across issue domains.
Future research could also examine the cumulative effects of repeated messages.
Our studies tested only the effects of isolated interest group interventions. Actual
communication campaigns, in contrast, often involve numerous interventions, and
it would be too easy to assume that repeated interventions have simple additive
effects. Initially successful persuasive messages are likely to exhibit decreasing mar-
ginal effects, as support cannot increase indefinitely. These effect ceilings determine
the total effects communication campaigns can accumulate. Research on repeated
exposure to the persuasive interventions will allow important insights into the per-
suasive power of interest group communication.
We have argued that sources with low public profiles do not have to worry about
source-related predispositions weakening the persuasive impact of their messages,
nor can they rely on source-related predispositions bolstering those messages. While
our argument and empirical tests focused on interest groups, this distinction of ef-
fect patterns based on varying strengths of public profiles is likely to be broadly ap-
plicable. It also likely holds for communicative interventions by other low-profile
actors who, given the affordances of digital communication environments, have
come to feature very prominently in contemporary public discourse (Jungherr,
Rivero, & Gayo-Avello, 2020). One prominent example of this can be found in the
wide variety of “alternative” sources challenging scientific and governmental bodies
with respect to epidemiological diagnoses and policies in the response to public
health crises. If communicative interventions by these low-profile actors follow the
same dynamics identified here, high-profile sources such as governmental organiza-
tions face a considerable challenge in reaching doubters while low-profile sources
such as alternative information providers on digital channels can count on broad
reach across populations.
Low-profile information sources of many different sorts are a consistent feature
of contemporary communication environments. As we have shown in this article,
communication research must account for their specific characteristics to understand
their persuasive appeal and influence in contemporary public opinion formation.
Supporting Information
Additional Supporting Information—such as questionnaires, treatment materials,
and supporting analyses—may be found in the online Appendices available in the on-
line version of this article.
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Notes
1. Data from Media Cloud (https://mediacloud.org) for search terms “National Rifle
Association,” “Republican Party,” and “Democratic Party” in sources New York Times,
USA Today, and Washington Post for mentions between 1 January and 31 December
2019.
2. Party systems feature parties that are marginal and have a very low public profile. Our
argument on the communicative situation of low-profile interest groups is likely also to
apply to low-profile political parties. To keep things simple, however, we ignore this vari-
ation in public profiles among political parties in the remainder of the article.
3. Data from Media Cloud for search terms “Greenpeace,” “Arbeitgeberverband
Gesamtmetall,” “CDU,” “SPD,” “Die Gru¨ nen,” and “FDP” in source set “German Media,
National” for mentions between 1 January and 31 December 2019.
4. Several cues could allow recipients to form ad-hoc assessments. For instance, the name
or the logo of an interest group might provide information recipients can use to evaluate
the source.
5. In a CATI survey representative of the German electorate conducted for us by the com-
pany Infratest dimap, only 10.8% of respondents indicated that they felt very or some-
what familiar with the political position of Gesamtmetall. At the same time, the share of
respondents who reported familiarity with a non-existing, fictional employers’ group
was only slightly lower (6.6%). In comparison, a larger share of respondents, 26%, felt
very or somewhat familiar with the political positions of Greenpeace, and 19.2% claimed
to be very or somewhat familiar with the political positions of Germany’s metal worker
union (see Appendix S1 for a detailed description of the survey and distributions of
answers). This indicates a low public profile for Gesamtmetall.
6. See Appendix S11 for replication with the full sample.
7. Regression tables are provided in Appendix S10.
8. To enable the use of our findings in subsequent third-party meta-analyses, we report
standardized coefficients in Appendix S12.
9. More technically, the coefficients for the field condition in the figures are ITT (intent to
treat) effects; the coefficients for the survey condition are ATE (average treatment
effects).
10. All p-values are from two-tailed tests.
11. A close analysis of the arguments listed by respondents suggests that the increase in the
aggregated measure is indeed driven by the specific arguments raised in the letter.
12. Credibility assessments of Gesamtmetall are, unfortunately, not available in this survey.
13. The full regression tables are provided in Appendix S10.
14. This finding also holds if we assume non-linear interaction effects (see Appendix S13).
15. The hypotheses, survey design, and analysis syntax of Study 2 were preregistered (except
for Hypothesis 2c, which was introduced following reviewer comments). See Appendix
S14 for details of the preregistration and deviations from the plan.
16. List available at https://www.umweltbundesamt.de/publikationen/flyer-anerkannte-
umweltvereinigungen.
17. Data from Media Cloud for mentions of interest group names between 1 January and 31
December 2019 in media source set “German Media, National.”
18. See Appendix S17 for detailed findings.
19. See Appendix S25.1 for full documentation of the underlying regression analyses and un-
derlying distributions.
20. The hypotheses, survey design, and analysis syntax of Study 3 were preregistered. See
Appendix S18 for details of the preregistration and deviations from the plan.
21. See Appendices S20–S24 for details.
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22. As a corollary of the unexpected main effects of the treatments, the data also do not lend
support for our expectation that the informational text should have nearly identical
effects when attributed to the low-profile interest group and when attributed to no
source. The preregistered equivalence tests yielded inconclusive results and thus did not
indicate with sufficient certainty that the differences between these two treatment groups
were below the pre-specified smallest effect size of interest.
23. It is important to note that these results are the same if we test party affiliation (see
Appendix S25) or political ideology (see Appendix S26) as moderators of treatment
effects rather than source credibility. This further supports our argument that party iden-
tification or political ideology do not have to be relevant predispositions in assessing the
persuasive power of interest groups.
Acknowledgments
We thank Antonin Finkelnburg and Ralf Gu¨ldenzopf in particular for their support
in realizing this project. We also thank Kevin Collins, Matthias v. der Malsburg, and
Peter Selb for helpful comments on the experimental design of our studies, Frederik
Aust, Aaron Caldwell, and Danie¨l Lakens for helpful comments on the power calcu-
lation for our third study, and Tim Andler, Scott Cooper, and Lukas Isermann for
assistance in the preparation of the manuscript. The complete data set, preregistra-
tion, and replication materials are available in Jungherr et al. (2020).
Funding
This research received funding from the Konrad-Adenauer-Stiftung (KAS), the
Arbeitgeberverband Gesamtmetall, and the University of Konstanz’s Young Scholar
Fund (YSF). These partners had no role in the analyses underlying this article and
imposed no restrictions in the presentation of the findings.
Conflicts of Interests
The authors declared no potential conflicts of interest with respect to the research,
authorship, and/or publication of this article.
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