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Dynamic Persuasion: Decay and Accumulation ofPartisan Media Persuasion
Zachary Markovich∗ Matthew A. Baum† Adam J. Berinsky‡
Justin de Benedictis-Kessner§ Teppei Yamamoto¶
January 22, 2020
Preliminary version prepared for the2020 Southern Political Science Association Conference
Abstract
The single shot nature of experiments on the effects of partisan media on public opinionmay limit the relevance of estimates that such studies produce for politics and policy.For example, there might be cumulative effects from multiple doses of partisan me-dia such that the combined effect of repeated exposures on political attitudes is muchgreater than that of a single dose. Similarly, the persuasive effect of partisan mediamight be temporary and decay quickly after a single exposure. We implement a novelmulti-wave experiment that allows us to examine these concerns. We find that the per-suasive effects demonstrate substantial durability, decaying only mildly over the courseof a week following treatment. Additionally, we find no evidence of cumulative effectsof repeated exposure to partisan media, and instead slight moderation. Together, theseresults suggest that partisan media’s influence on public opinion is persistent, but theadditive effects of “filter bubbles” are limited.
We appreciate the research assistance of Grace Chao, Henry Feinstein, and Kaitlin Tucci, and fundingfrom the National Science Foundation (SES-1528487) and the Political Experiments Research Lab (PERL)at MIT.∗PhD student, Department of Political Science, Massachusetts Institute of Technology, [email protected]†Kalb Professor, John F. Kennedy School of Government, Harvard University,
Matthew [email protected]‡Mitsui Professor, Department of Political Science, Massachusetts Institute of Technology,
[email protected]§Assistant Professor, Department of Political Science, Boston University, [email protected]¶Associate Professor, Department of Political Science, Massachusetts Institute of Technology,
Introduction
Statements by pundits, politicians, and citizens alike lament the rise of political polarization
and the role that partisan news media may have played in this process. The proliferation of
choices in both television and online media allows for individuals to select into ideologically
consonant news sources – selective exposure (e.g. Lazarsfeld, Berelson, and Gaudet, 1948;
Sears and Freedman, 1967) – and potentially may lead to consumption of exclusively one-
sided news content (Groeling, 2013). Over time, this might lead to people believing this
one-sided version of issues without attention to the multifaceted nature of reality.
Recent research has shown that such ideological self-selection does occur (Arceneaux,
Johnson, and Murphy, 2012; Gaines and Kuklinski, 2011; Iyengar and Hahn, 2009; Stroud,
2011), though it may not be as extensive as previously assumed (Bakshy, Messing, and
Adamic, 2015; Brundidge, 2010; Guess, 2018; Messing and Westwood, 2014; Mummolo,
2016). Other research has suggested that, in addition to polarization resulting from selec-
tive exposure, partisan media itself may further polarize people’s attitudes (Bullock, 2011;
de Benedictis-Kessner et al., 2019; Dilliplane, 2014; Feldman, 2011; Levendusky, 2013b).
This may crucially depend on the degree to which the people exposed to such partisan me-
dia might self-select into consuming that media on their own (de Benedictis-Kessner et al.,
2019; Leeper, 2017).
Zaller’s (1992) theory of opinion change also suggests that experimental observations of
persuasion by partisan media may occur because such experiments make certain considera-
tions more accessible to survey respondents. Experimental results indicating the moderation
of persuasion effects by media preferences may be a consequence of those considerations be-
ing differentially accessible to different types of media consumers. This would suggest that
such persuasion effects are artificial and would quickly decay, in contrast with more long-
lasting opinion changes from new information (Coppock, 2017; Coppock et al., 2018). Such
competing theories of opinion change present contrasting normative implications: if survey
experimental treatment effects quickly decay, they are less of a problem for democracy than
1
if they are persistent (Gaines, Kuklinski, and Quirk, 2007).
Single-exposure experiments are inherently limited in their ability to detect such the-
oretical processes as they ordinarily cannot assess the long-term impacts of experimental
treatments. In this paper, we avoid this problem by conducting a large-scale multiwave
experiment that tests for both the accumulation of media persuasion and the decay of such
persuasive effects. We find that partisan media has limited cumulative effect when people
are experimentally exposed to such treatments multiple times relative to a single time over
the course of multiple weeks. In addition, we find that the persuasion effects of partisan
media only decay slightly over the course of a week. These results indicate, in the framework
of Zaller (1992), that partisan media may provide additional considerations to consumers
rather than simply making certain considerations more accessible. These results support
a theory of opinion change that explains previous findings on the moderation of partisan
media persuasion and extend theory to longer time horizons. Consequently, our work recon-
ciles previous experimental findings with both real-world patterns of polarization and public
opinion theory. Moreover, our results suggest that partisan media’s persuasive impact may
be especially potent and long-lasting among the people who have fewer previous considera-
tions. This may consequently lead to more severe polarization and problems for democratic
accountability.
Accumulation of Partisan Media’s Effects
Most people who watch or read partisan media do so repeatedly. Studies examining the
effects of a single exposure to partisan news therefore are limited in their ability to predict
real-world effects of such media (Slater, 2004). Limited studies, however, have used ex-
perimental designs incorporating multiple exposures to partisan news and assessed whether
repetition of the arguments contained in partisan news has an additive or cumulative ef-
fect. This research has pointed to limited accumulation of persuasive effects after repeated
2
exposure to media dependent on the content, circumstances, and individuals receiving infor-
mation.
In one example of such research, Levendusky (2013a) shows survey respondents either
like-minded partisan news editorials or apolitical articles in a two-wave experiment. His
effects demonstrate that multiple exposures to like-minded partisan media can polarize peo-
ple’s attitudes more than just a single exposure, but that this effect is smaller than the initial
effects of (novel) political news. Thus we might expect that persuasion effects compound
after multiple exposures relative to single exposure to partisan media. Similar research test-
ing the effects of repeated exposure to political media indicates limits to this accumulation,
and suggests that repeated exposure may have no effect beyond that of a single exposure
(Lecheler and de Vreese, 2013). This research is in line with communication theory predicting
that repeated framing of information may be redundant (Baden and Lecheler, 2012).
Limited accumulation of persuasion effects may be due to qualities of both the indi-
vidual and the information being presented. For instance, “pretreatment” effects of the
prior exposure to partisan media that limit the degree of attitude change that can occur
subsequently (Druckman and Leeper, 2012). Similarly, if individuals are exposed to cross-
cutting arguments that counter one another with competing messages, repetitive exposure
may not have an additional impact on attitudes or beliefs (Chong and Druckman, 2010).
Thus individuals’ prior exposure may moderate the cumulative nature of persuasion effects
(de Benedictis-Kessner et al., 2019; Huber and Arceneaux, 2007; Zaller, 1992). This would
lead us to expect large initial effects and large effects among those with limited previous ex-
posure, but little additional impact of repeated treatment by partisan media. The message
itself may also influence the accumulation of attitude change. Negatively framed information
may be more effective when repeated, while positively framed information is not (Lecheler
et al., 2015). Similarly, if the topic of information is relevant to individuals (Cacioppo and
Petty, 1979; Liu et al., 2019) or the argument contained in that information is stronger (Ca-
cioppo and Petty, 1989), multiple exposures to a certain framing of that information may
3
be more persuasive than a single exposure.
Persistence and Decay
Partisan media’s persuasive effects over time may accumulate, but they may also decay.
If persuasion effects are short-lived they may not be as critical a problem for democratic
deliberation than if they are persistent (Gaines, Kuklinski, and Quirk, 2007). Identifying
the long-term potentially pernicious persistence of persuasion effects is a crucial step to
understanding the role of the media in reality.
Previous work on informational framing in news articles indicates that experimental
estimates of persuasion may be quite persistent.1 Partisan media’s polarizing impact, in
particular, may endure for at least two days (Levendusky, 2013a, p. 85-86). Some persuasion
may only decay in size by approximately half over ten days, and persist at that level for up to
a month (Coppock et al., 2018). This may be due to the content of the information presented
to people. Persuasion may be especially persistent if it provides new information to people
rather than simply framing existing information (Coppock, 2017), or if it negatively frames
information (Lecheler and de Vreese, 2011). Partisan media’s content often involves the
provision of new information as well as persuasive arguments, and so its persuasive effects
may be persistent.
Some examinations of this question suggest that persuasion effects may decay, but only
in certain segments of the population — such as those who are high in “need for cogni-
tion” (Chong and Druckman, 2010), or moderate in levels of political knowledge (Baden
and Lecheler, 2012). Such individual-level characteristics may moderate the persistence of
partisan media’s influence.
On the other hand, research on campaigns and highly polarized policy issues suggests a
1One related theory in research on media effects that we do not discuss at length here argues that the per-suasive impact of political communication will not manifest immediately, but will have a delayed “sleepereffect” (e.g. Hovland, Lumsdaine, and Sheffield, 1949; Hovland and Weiss, 1951). More recent examina-tions of the sleeper effect, however, have struggled to show any evidence of its existence except in limitedcircumstances (Capon and Hulbert, 1973; Coppock, 2017; Gillig and Greenwald, 1974; Jensen et al., 2011).
4
different conclusion on the persistence of persuasion. Hill et al. (2013) show that presidential
campaign advertisements have short-lived effects on attitudes that decay by 50% after 4
days, but that still persist even 6 weeks later, albeit with small effect sizes. Thus, in highly
salient campaigns, political persuasion by advertisements may be minimally persistent. Hill
et al. (2013) also show that the persistence of political advertising’s effects is even smaller in
lower-level (Senate, House, and gubernatorial) elections. Similarly, Dowling, Henderson, and
Miller (2019) show that while informational treatments about the Affordable Care Act can
durably affect people’s levels of knowledge about policy-related facts, the effects on policy
attitudes do not persist even one week later. Likewise, the effects of news information on
evaluations of government may also dissipate within a single week (Kalmoe et al., 2019).
Thus in both low-salience elections and on policy issues, attitudinal persuasion may be
short-lived. Partisan media’s effects on policy attitudes such as those we examine here may
therefore decay quickly.
Research Design and Data
To assess these questions, we conduct a large-scale experiment embedded within a three-wave
panel survey using a version of the PICA design (de Benedictis-Kessner et al., 2019; Knox
et al., 2019) adapted for a multi-wave context. A visual diagram of this adapted design is
presented in Figure 1, showing the first wave at the top, the second wave in the middle, and
the final wave at the bottom.
In this design, we first measure the stated preference of all respondents over three media
options early in the survey. Specifically, we asked: “If you were given the choice of news
articles from the following three sources to read, which of the three would you choose?” We
presented each choice with an accompanying logo of the network, while randomizing the
order in which the options appeared on the screen. We then move to a “washout” period,
where we asked participants to answer demographic questions not directly related to the
5
Figure 1: Experimental Design
Wave 1 W1 “forced exposure” condition
randomize and assigntreatment
MSNBC
Entertainment
Fox
measureW1
outcomes
measurestated
preference“washout”
periodrandomize
designs
MSNBC
Entertainment
Fox
W1 “free choice” condition
measure and assignrevealed preference
MSNBC
Entertainment
Fox
Wave 2 W2 “forced exposure” condition
randomize and assigntreatment
MSNBC
Entertainment
Fox
measureW2
outcomes
measurestated
preference“washout”
periodrandomize
designs
MSNBC
Entertainment
Fox
W2 “free choice” condition
measure and assignrevealed preference
MSNBC
Entertainment
Fox
Wave 3
measureW3
outcomes
media choice, and to complete distraction tasks.2 We then randomly assign participants
to either a forced exposure or a free choice treatment condition in each of the first two
waves. Those in the forced exposure condition were assigned to read one of three news
reports, while those in the free choice condition were allowed to choose one of these media
options.3 Participants in both conditions then read their assigned or chosen news reports
from either Fox News, MSNBC, or an entertainment network (the Food Network) that we
created from real online news stories and then edited to equalize their length and framing.
2The goal was to minimize the possibility that measuring stated preferences might contaminate respondents’voluntary choices later in the survey. These distraction tasks enhance external validity by allowing for theinstability of preferences over time.
3For those in the free choice arm, we asked, “Which of these three articles would you like to read now?”
6
For the partisan media treatments, the articles discussed either the economic, social, safety,
or public health effects of legalizing marijuana. On each topic, the Fox News and MSNBC
articles were nearly identical except for text that was either supportive of (MSNBC) or
opposed to (Fox) marijuana legalization. The Food Network articles discussed how to save
money while grocery shopping, tips for buying meat, and how grocery stores might change
in the future.
Finally, we asked respondents a number of questions measuring their opinions about mar-
ijuana policy and anticipated behavior regarding the stories they had read. Specifically, in all
three waves we asked respondents ten questions about their policy preferences on marijuana
and drugs. We asked them if they agreed or disagreed with the following statements, “The
legalization of marijuana leads to fewer people using more serious drugs, such as heroin
and cocaine” and “Marijuana use increases violent crime,” corresponding to the articles
about public safety and health consequences of legalization. Similarly, we asked respondents
whether legalization would make the economy better or worse, which corresponded directly
to the interventions about the tax and economic implications of legalization. Other ques-
tions addressed feelings regarding marijuana more broadly. Respondents placed themselves
on 7-point scales between strongly agreeing or strongly disagreeing with the phrases: “Gov-
ernment efforts to enforce marijuana laws cost more than they are worth,” “Using marijuana
is morally wrong,” “Marijuana should be legal for medical use,” “Marijuana use is a serious
problem today,” and “Marijuana should be legal for recreational use.” Finally, respondents
placed themselves along another seven-point scale between, at one end, whether habitual
drug use should be thought of as a criminal offense or, at the other, a medical problem.
They then placed several substances, including marijuana, on scales from very dangerous
to very safe. We recode all opinion variables to 0-1 intervals, with the most liberal or per-
missive of legalization at 0 and the most conservative or opposing of legalization at 1. To
capture variation in underlying latent attitudes and beliefs about marijuana, we form an
internally-consistent additive index of these ten opinion questions (α = 0.89). We use this
7
index as the primary dependent variable on which we assess polarization and persuasion.
In the first two waves, we also asked respondents to indicate their likelihood of forwarding,
discussing, posting to social media, or seeking out additional information on the story they
had just read. We combined these four measures into an additive index of sharing behavior,
which ranges from 0 (least likely to share) to 1 (most likely to share).
We administered this experiment via an online survey to a national sample of respondents
recruited through Survey Sampling International (SSI).4 In the first wave, this consisted of
7,393 survey respondents in the first wave, 4,926 in the second wave, and 4,526 in the third
wave. Respondents to the first two waves were invited to participate in the next wave one
week after they had completed the previous survey wave. This yielded a final retention rate
in the third wave of 61.2%.
Using these data, we assess the persuasive treatment effects of partisan media, as well
as the decay and the cumulative nature of these treatment effects with a series of models.
First, to assess immediate persuasion effects, we fit the following model:
Marijuana indexij = β0 + β1Treatij (1)
where i designates respondents and j designates experimental waves. This specification thus
examines the causal effect of a given media treatment on attitudes measured immediately
afterwards, collapsing across the first two waves in our experiment.
We also consider whether partisan media’s persuasive effects varied by respondents’ stated
media preferences. To do this, we interacted their stated media preference with the treatment
received using the following model specification:
4SSI recruits participants through various online communities, social networks, and website ads. Whendeploying a particular survey, SSI randomly selects participants for survey invitations. We asked SSI torecruit a target population that matched the (18 and over) census population on education, gender, age,geography, and income. The result is a diverse national sample, albeit not a probability sample.
8
Marijuana indexij = β0 + β1Media Preferenceij + β2Treatij + β3Treatij ×Media Preferenceij
(2)
Next, we assess the decay of these treatment effects by regressing the outcome measured
in wave j + 1 on the treatment in wave j. These models take the following form:
Marijuana indexi,j+1 = β0 + β1Treatij (3)
such that we measure the effect of treatment in wave 1 on wave 2 outcomes and the effect
of treatment in wave 2 on wave 3 outcomes.
We also assess the cumulative impact of partisan media using our multiwave panel. We
examine whether treatment with the same type of media twice results in a greater change in
respondent opinions than after treatment only once, or if there are no such additive effects.
To examine this type of accumulation, we fit the following model:
Marijuana Index Wave 2i = β0+β1Treatment Wave 1i+β2Treatment Wave 2×Treatment Wave 1i
(4)
This approach allows for there to be significant heterogeneity in the effect of treatment
with different kinds of media, but limits our statistical power for certain analyses as some
subgroups of the analysis are relatively rare.5
5For example, people who prefer MSNBC but were exposed to Fox News twice comprise under one twenty-seventh of our full forced choice arm.
9
Results
Persuasion Effects
We begin our analysis by replicating previous findings about the short term persuasive
effects of partisan media in a single round experiment. We present estimates for the effect
of partisan media on attitudes expressed in the same wave in Table 1. Our results reveal a
clear persuasive effect of partisan media. The forced choice results indicate that respondents
who read Fox News or the entertainment article rather than MSNBC reported attitudes that
were significantly more conservative. In particular, the effect of reading Fox News rather
than MSNBC is approximately the same size as the attitudinal difference between responses
from Democrats and independents in the free choice arm of our first wave.
Table 1: Media Persuasion Effects, Waves 1 and 2 pooled
Dependent variable:
Attitudinal Index
Entertainment 0.013∗
(0.008)
Fox 0.031∗∗∗
(0.008)
Constant 0.357∗∗∗
(0.005)
Observations 5,173
Note: ∗p<0.1; ∗∗p<0.05; ∗∗∗p<0.01
Effect Heterogeneity By Media Preference
We next present our forced choice group results disaggregated by respondents’ stated pref-
erences. Figure 2 shows the persuasive effects of Fox relative to MSNBC in our three stated
10
preference groups for the first and second waves pooled. In both survey waves, those re-
spondents who preferred Fox and MSNBC who were assigned the Fox article reported more
conservative opinions than respondents that read the MSNBC article. In contrast, among
those respondents who preferred entertainment, there was a more muted persuasion effect.6
●
●
●
● ●
●
Attitudinal Index Sharing Index
PreferEntertainment
PreferFox
PreferMSNBC
PreferEntertainment
PreferFox
PreferMSNBC
−0.15
(Moreliberal)
−0.10
−0.05
0.00
0.05
(Moreconservative)
0.10
−0.15
(Lesswillingnessto share)
−0.10
−0.05
0.00
0.05
(Greaterwillingnessto share)
0.10
Trea
tmen
t effe
ct o
f rea
ding
Fox
rat
her
than
MS
NB
C, W
1/W
2 co
llaps
ed
Figure 2: Persuasion Results, Wave 1 and 2 pooled
We present these results pooling treatment in both wave 1 and wave 2 on the same-wave
attitudes in tabular form in Table 2. The treatment effect of exposure to Fox News rather
than MSNBC, shown in the second line of the table, is positive and statistically significant
in the groups of respondents who preferred Fox or MSNBC, but not those who stated a
preference for entertainment. 7
6If the two waves are pooled together (as we do here and in Appendix Table A1), the results suggestsignificant persuasive effects among Fox and MSNBC prefers but not among those who prefer entertainment.However, when we disaggregate the two waves in Appendix ??, we find a statistically significant effect amongentertainment preferrers in wave 1.
7In addition, in Appendix A we present analyses examining the heterogeneity in the effect sizes amongstated preference subgroups. The small interaction terms in the models suggest little heterogeneity in ourtreatment effects by respondents’ stated media preferences.
11
Table 2: Immediate Persuasion Effects, Stated Preference Subgroups
Prefer:Entertainment Fox MSNBC
(1) (2) (3)
Entertainment 0.006 0.010 0.020(0.013) (0.012) (0.013)
Fox 0.017 0.039∗∗∗ 0.034∗∗∗
(0.013) (0.012) (0.013)
Constant 0.345∗∗∗ 0.420∗∗∗ 0.285∗∗∗
(0.009) (0.009) (0.009)
Observations 1,576 2,083 1,516
Note: ∗p<0.1; ∗∗p<0.05; ∗∗∗p<0.01
Decay of Persuasive Effects
We next examined the durability of these persuasive effects. In Figure 3 we show these
results using the treatment in one wave on outcomes in the following wave. 8 Comparing
these figures to Figure 2, we can see that the treatment effects of Fox relative to MSNBC
are similar when measured with same-wave attitudes as when measuring attitudes in the
following wave. These results suggest that partisan media’s persuasive effects decay only
slightly over the course of one week.
We also present these results in Table 3, pooling across waves of the survey and respondent
preference subgroups, in order to look at the holistic effect of treatment in wave j on outcomes
in wave j + 1.
These results further demonstrate the mild decay in the size of persuasion effects between
waves. The treatment effect of reading Fox News rather than MSNBC from the forced choice
8We also present results not collapsed across the two waves of treatment in the Appendix, where we examinethe effects of treatment in wave 1 on outcomes in wave 2, using only the free choice arm of wave 2. as wellas the effect of treatment in wave 1 on outcomes in wave 3, and treatment in wave 2 on outcomes in wave3.
12
●
● ●●
●
●
Attitudinal Index Sharing Index
PreferEntertainment
PreferFox
PreferMSNBC
PreferEntertainment
PreferFox
PreferMSNBC
−0.15
(Moreliberal)
−0.10
−0.05
0.00
0.05
(Moreconservative)
0.10
−0.15
(Lesswillingnessto share)
−0.10
−0.05
0.00
0.05
(Greaterwillingnessto share)
0.10
Trea
tmen
t effe
ct o
f rea
ding
Fox
rat
her
than
MS
NB
C o
n ne
xt w
ave,
W1/
W2
colla
psed
Figure 3: Effects of Partisan Media on Next Wave Outcomes
arm of the experiment declines by only 24 % relative to the estimate of treatment on attitudes
measured immediately following media exposure from Table 1. These small decreases in the
size of our treatment effects over the course of a week suggest that even a single dose of
partisan media may have more long-lasting effects than has been frequently assumed.9
Table 4 shows these results disaggregated by respondent’s media preferences. These
results uncover some heterogeneity in the decay of partisan media’s treatment effects. In
particular, the treatment effect of partisan media among people who prefer entertainment
appears to decay more than among other groups of media consumers. The effect of treatment
with Fox rather than MSNBC on respondents’ attitudes in the next wave is statistically
indistinguishable from zero among the group of respondents who stated a preference for
9One concern with this modeling approach is that it might overstate the effect of treatment in wave 1 onopinion in wave 2 if treatment in wave 1 also impacts the media choices of the free choice arm respondentsin wave 2. For example, if respondents treated with Fox News in wave 1 were more likely to choose Fox newsagain in wave 2, this modeling approach would overstate the persuasive effect of treatment with Fox Newsin wave 1. To avoid this concern, we can assess the decay of the effects of treatment in wave 2 on wave 3outcomes given that the third wave of our survey included no media choice or exposure. We assess whetherthe size of these lagged effects differs between waves in Appendix C, and our results indicate no significantheterogeneity in the size of the effect decay between waves, suggesting that this concern is unlikely to beproblematic.
13
Table 3: Decay of Media Persuasion Effects, All Respondents
Dependent variable:
Next Wave Attitudinal Index
Entertainment 0.002(0.010)
Fox 0.023∗∗
(0.010)
Constant 0.370∗∗∗
(0.007)
Observations 3,199
Note: ∗p<0.1; ∗∗p<0.05; ∗∗∗p<0.01
entertainment. In comparison, the effects of treatment on respondents’ attitudes in the
next wave among those who prefer MSNBC and those who prefer Fox are more durable.
Respondents preferred either partisan news option and who read Fox rather than MSNBC
reported attitudes that were still more conservative in the following wave. In both cases
these effects are statistically significant and their size is on par with the immediate effects
of partisan media.
14
Table 4: Decay of Media Persuasion Effects, Media Preference Subgroups
Prefer:Entertainment Fox MSNBC
(1) (2) (3)
Entertainment −0.014 −0.001 0.023(0.017) (0.015) (0.017)
Fox −0.00004 0.032∗∗ 0.040∗∗
(0.017) (0.016) (0.017)
Constant 0.362∗∗∗ 0.436∗∗∗ 0.285∗∗∗
(0.012) (0.011) (0.012)
Observations 931 1,316 953
Note: ∗p<0.1; ∗∗p<0.05; ∗∗∗p<0.01
Cumulative Persuasion Effects
We next assess whether the impact of partisan media accumulates after multiple treatments
one week apart. We first examine the treatment effect of one extreme relative to another:
treatment with Fox in both waves rather than MSNBC in both waves. We plot these effects
of double treatment in Figure 4 along the vertical axis, disaggregated by respondents’ stated
preferences along the horizontal axis, using only respondents who were in the forced choice
arm of the experiment in both waves.
These results indicate little added impact of a second treatment on attitudes, and in fact
perhaps some regression to the mean after two treatments. Across all preference subgroups of
respondents, there are no statistically significant effects of treatment with Fox twice relative
to MSNBC twice. This contrasts with the results from the previous section, indicating that
the effects from one wave of treatment on attitudes are durable from one wave to the next.
The results in this section indicate that, following a second (forced) treatment with partisan
media, opinions may return to previously held viewpoints. The lack of differences between
groups treated twice with oppositional partisan media is evidence of a limit on attitudinal
15
●
●●
●
●
●
Attitudinal index W2 Sharing index W2
PreferEntertainment
PreferFox
PreferMSNBC
PreferEntertainment
PreferFox
PreferMSNBC
−0.30
(Moreliberal)
−0.20
−0.10
0.00
0.10
(Moreconservative)
0.20
−0.30
(Lesswillingnessto share)
−0.20
−0.10
0.00
0.10
(Greaterwillingnessto share)
0.20
Trea
tmen
t effe
ct o
f rea
ding
Fox
twic
e ra
ther
than
MS
NB
C tw
ice
Figure 4: Effect of Wave 1 and Wave 2 Treatment on Wave 2 Outcomes
polarization from repeated exposure.
How does this compare to people who received only one “dose” of partisan media across
the two waves? In Figure 5 we plot the treatment effect on attitudes, comparing the group
of people assigned to read Fox once (and entertainment media in the other wave) to the
group assigned to read MSNBC once (and entertainment media in the other wave). These
effects, in contrast, indicate a small persuasive effect on all subgroups of respondents, though
these effects are not statistically significant. This further corroborates the interpretation of
the previous effects as evidence that one dose of partisan media may polarize attitudes, but
additional exposure does not further polarize opinions.
To examine the accumulation of partisan media’s persuasive effects more systematically,
we assess whether our treatment effects of one exposure to partisan media differ from our
treatment effects from multiple exposures in a pooled format. In Appendix D, we present
the results of pooled analyses of cumulative effects. These analyses suggest little evidence
of cumulative persuasion effects. This suggests that there is little additional effect from
16
●
●
●
●
●
●
Attitudinal index W2 Sharing index W2
PreferEntertainment
PreferFox
PreferMSNBC
PreferEntertainment
PreferFox
PreferMSNBC
−0.10
(Moreliberal)
−0.05
0.00
0.05
(Moreconservative)
0.10
−0.10
(Lesswillingnessto share)
−0.05
0.00
0.05
(Greaterwillingnessto share)
0.10
Trea
tmen
t effe
ct o
f rea
ding
Ent
erta
inm
ent +
Fox
once
rat
her
than
Ent
erta
inm
ent +
MS
NB
C o
nce
Figure 5: Effect of Wave 1 and Wave 2 Treatment on Wave 2 Outcomes
multiple treatments with the same partisan media.10
10Interestingly, respondents who were treated with MSNBC twice reported more conservative opinions rel-ative to the baseline of respondents treated with MSNBC just once, although this trend falls short ofstatistical significance.
17
Polarization of Future Media Choices
Finally, we assess how partisan media affects future media choices. We find evidence suggest-
ing an impact of treatment with partisan media on future media consumption choices, but
it is limited to the segment of people who would not ordinarily consume partisan political
news. Tables 5 and 6 show the distribution of wave 2 media choices by the article read in
wave 1. Table 5 limits the results to respondents in the forced choice condition in wave 1
while Table 6 shows the results for respondents in the free choice condition in wave 1. Both
tables are limited to the respondents in the free choice condition in wave 2 and the outcome
is the actual article chosen and read by respondents rather than stated preferences. Because
wave 1 treatment was randomized for the group in Table 5, the values in the table repre-
sent unbiased estimates of the effect of partisan media consumption on future media choice.
In contrast, the results in Table 6 are more likely to reflect preexisting preferences among
the consumers of each kind of partisan media (in other words, how enduring the preference
people have for Fox News/MSNBC/Entertainment media might be one week later).
Wave2 ChoiceMSNBC Entertainment Fox
MSNBC 0.32 0.27 0.41Wave 1 Forced Article Entertainment 0.29 0.33 0.38
Fox 0.30 0.32 0.37
Table 5: Fraction of Wave 2 Free Choice Respondents Choosing Each Media Type by RandomWave 1 Treatment
The results in Table 5 suggest a small effect of partisan media exposure on future media
choices. Among respondents given their choice of media in wave 2, Fox News is the most
popular choice. Curiously, a larger fraction of respondents assigned MSNBC in wave 1
consume Fox News in wave 2 (41%) compared to those assigned Fox in wave 1 do (37%).
Overall, respondents only choose to read the same media in wave 2 they were assigned in
wave 1 32% of the time, suggesting no tendency to consume the same media in both waves.
The chi-squared test fails to reject the null hypotheses that the article assigned in wave 1 is
18
independent from the article read in wave 2 (p ≈ 0.4). This provides evidence that across
the entire sample, partisan media exposure did not influence future choices.
We present these results graphically in Figure 6, with respondents’ assigned media in
the first wave on the left and their chosen media in the second wave on the right, using
respondents who were in the forced choice arm in wave 1 and the free choice arm in wave
2. The color of each alluvium in the plot corresponds to their chosen media in the second
wave of the survey, and comparing the size of the alluvia of the same color between different
forced choice groups in wave 1 on the left represents the treatment effect of media exposure.
MS
NB
CF
ox
En
tert
ain
me
nt
MS
NB
CF
ox
En
tert
ain
me
nt
0
300
600
900
1200
W1 Media Assigned W2 Choice
Media Read, Forced Choice W1/Free Choice W2
Fre
q
Figure 6: Forced Choice W1 Respondents’ Future Choices
Wave2 ChoiceMSNBC Entertainment Fox
MSNBC 0.73 0.16 0.11Article Chosen Wave 1 Entertainment 0.10 0.73 0.16
Fox 0.08 0.14 0.78
Table 6: Fraction of Wave 2 Free Choice Respondents Choosing Each Media Type by Wave1 Article Free Choice
In contrast, respondents in the free choice arm of our experiment in both waves indicated
an overwhelmingly tendency to consume the same media in both waves, which we show in
19
Table 6. This trend was strongest among respondents who consumed Fox News in wave 1.
Of this group, 78% of respondents chose to read Fox News in wave 2 again. Similarly, 73%
of respondents who chose to read MSNBC in wave 1 again chose to read MSNBC in wave
2 and 73% of respondents who chose to read entertainment in wave 1 also chose to read
entertainment in wave 2. We show these patterns in visual form in Figure 7, using only
respondents who were in the free choice arm in both wave 1 and wave 2, with the color of
the alluvia corresponding to the choice of media in the first wave. The small defection rates
are demonstrated by the lack of large alluvia moving from any wave 1 choice group to a
different wave 2 choice group. This gives some evidence that media choices remain relatively
stable over the period of a week in a free choice scenario.
MS
NB
CF
ox
En
tert
ain
me
nt
MS
NB
CF
ox
En
tert
ain
me
nt
0
300
600
900
1200
W1 Choice W2 Choice
Revealed Media Preference, Free Choice Arm
Fre
q
Figure 7: Free Choice Respondents’ Choices Over Time
Although consumers of partisan media are generally consistent in their media choices,
there is still a non-negligible rate of defection. 11% of respondents that chose MSNBC in
wave 1 chose to read Fox News in wave 2 while 8% of respondents that read Fox News in wave
1 chose to read MSNBC in wave 2. This suggests that people choose to expose themselves
to some amount of counter-attitudinal messaging, even if it is less common than continuing
to choose their preferred media. Together, these findings suggest that while consumers of
20
partisan media have a consistent preference for their preferred media, this tendency is not
driven by the persuasive effect of partisan media.
We examine the persuasive impact on future choices in a more systematic fashion in
Table 7. We use a multinomial logit model to assess the impact of wave 1 media treatment
on wave 2 media choice, using MSNBC as the baseline choice and showing the effect on
choosing Entertainment rather than MSNBC in column 1 and Fox rather than MSNBC in
column 2. This analysis is limited to respondents who were in the forced choice group in
wave 1, but the free choice group in wave 2. This table reveals no significant effects of wave
1 media treatment on wave 2 media choice, corroborating the trends revealed in the earlier
tables. The positive coefficients of treatment with either entertainment or Fox in the first
column indicate that they are slightly more likely to choose entertainment in wave 2, and
the small negative coefficients in the second column indicate they are less likely to choose
Fox. All of these effects on future media choice across the entire sample are statistically
indistinguishable from zero, however.
Table 7: Impact of W1 Media Assigned on W2 Media Choice
Dependent variable:
Entertainment Fox
(1) (2)
Entertainment 0.287 −0.005(0.189) (0.177)
Fox 0.223 −0.067(0.186) (0.174)
Constant −0.160 0.266∗∗
(0.137) (0.124)
Akaike Inf. Crit. 2,515.860 2,515.860
Note: ∗p<0.1; ∗∗p<0.05; ∗∗∗p<0.01
However, these overall null effects across the entire sample belie some group-specific
21
effects on future choices. Figure 8 shows the effects of treatment with partisan media on
choice in the next wave of the survey, disaggregated by respondents’ stated media preferences.
Each point represents the treatment effect of reading Fox rather than MSNBC in wave 1
on the probability of choosing a given media option in the free choice arm of wave 2, for
entertainment (in the left panel), Fox (in the middle), or MSNBC (on the right), divided up
by stated preference groups along the horizontal axis.
ChooseEntertainment, W2
ChooseFox, W2
ChooseMSNBC, W2
W1 PreferEntertainment
W1 PreferFox
W1 PreferMSNBC
W1 PreferEntertainment
W1 PreferFox
W1 PreferMSNBC
W1 PreferEntertainment
W1 PreferFox
W1 PreferMSNBC
-0.20
(Lesslikely to choose)
-0.10
0.00
0.10
(Morelikely to choose)
0.20
Tre
atm
en
t e
ffe
ct o
f re
ad
ing
Fo
x r
ath
er
tha
n M
SN
BC
in W
1
Figure 8: Effect of Wave 1 Treatment on Wave 2 Choices
These plots show that, for the most part, there is little effect of consuming partisan media
on future behavior, as measured by respondents’ actual choices of media when they were
allowed to select from these options. The only group of media consumers on which partisan
media seems to influence future choices is those respondents who stated a preference for
entertainment. Among these respondents, those who were assigned to read Fox in wave 1
were 12 percentage points less likely to choose Fox in wave 2 when given the choice than
those respondents who were assigned to read MSNBC in wave 1. In other words, this group
of people who would not ordinarily expose themselves to partisan media actively chose to re-
balance their media diets after a single exposure to partisan media. Among these consumers,
exposure to Fox caused them to avoid this choice in the future, relative to those who were
22
exposed to MSNBC, who were more likely to choose Fox in the future.
These effects on actual choices did not seem to extend to stated preferences in either
wave 2 or wave 3, however. Figures 9 and 10 show the effects of treatment with Fox relative
to MSNBC in wave 1 or wave 2 on respondents’ stated preferences in the following wave.
Across all subgroups in both waves, treatment with partisan media did not influence future
stated preferences.
PreferEntertainment, W2
PreferFox, W2
PreferMSNBC, W2
W1 PreferEntertainment
W1 PreferFox
W1 PreferMSNBC
W1 PreferEntertainment
W1 PreferFox
W1 PreferMSNBC
W1 PreferEntertainment
W1 PreferFox
W1 PreferMSNBC
-0.15
(Lesslikely to prefer)
-0.10
-0.05
0.00
0.05
(Morelikely to prefer)
0.10
Tre
atm
en
t e
ffe
ct o
f re
ad
ing
Fo
x r
ath
er
tha
n M
SN
BC
in W
1
Figure 9: Effect of Wave 1 Treatment on Wave 2 Stated Preferences
23
PreferEntertainment, W3
PreferFox, W3
PreferMSNBC, W3
W1 PreferEntertainment
W1 PreferFox
W1 PreferMSNBC
W1 PreferEntertainment
W1 PreferFox
W1 PreferMSNBC
W1 PreferEntertainment
W1 PreferFox
W1 PreferMSNBC
-0.15
(Lesslikely to prefer)
-0.10
-0.05
0.00
0.05
(Morelikely to prefer)
0.10
Tre
atm
en
t e
ffe
ct o
f re
ad
ing
Fo
x r
ath
er
tha
n M
SN
BC
in W
2
Figure 10: Effect of Wave 2 Treatment on Wave 3 Stated Preferences
Conclusion
The widespread proliferation of partisan political news media has led to worries about its
pernicious effects on polarization and the resulting problems for democracy. Recent research
has indicated that partisan media can potentially polarize consumers of the information that
they broadcast. Yet we have had little evidence of the dynamic long-term impact of partisan
news on political attitudes and choices. Understanding this long-term impact is crucial
for diagnosing potential consequences for both public opinion and democratic deliberation
(Gaines, Kuklinski, and Quirk, 2007).
In this paper, we provide the first examination of the long-term persuasive impact of
partisan media on policy attitudes that evaluates these effects within the context of individ-
uals’ choices over media options. We use a PICA experimental design (de Benedictis-Kessner
et al., 2019; Knox et al., 2019) adapted for a three-wave opinion survey that allows us to
disaggregate both our short-term and long-term estimates of persuasion by the preferences
of media consumers among different news options. Our results indicate both the extent and
limits of partisan media’s effects over time. While repeated exposure to partisan media has
24
limited cumulative effects on all types of consumers, the persistence of persuasion – even
from just one instance of experimental exposure to partisan media – suggests a long-term
impact of partisan media on public opinion.
Our results showing little accumulation of partisan media’s effects on political attitudes
support theories of political communication’s long-term influences on public opinion. The
fact that there is little additive effect from multiple instances of exposure to arguments
contained in partisan news stories suggests that there are limits to the political polarization
that can be attributed to partisan news. Pundits and politicians have decried the pernicious
effects of “filter bubbles” or “information silos” resulting from consumers’ ability to self-
select into news diets that only exposure them to slanted news from one side (Pariser, 2012;
Sunstein, 2001). The normative argument underlying these claims is that such one-sided
exposure to partisan news will have an impact on attitudes due to repeated reinforcement
of those arguments that subsequently drives polarization. In contrast, our results suggest
that the additive impact of repeated exposure to such news sources is no more extreme
than a single exposure to partisan news, and therefore likely is not the cause of additional
polarization among those who consume it repeatedly.
The effects of partisan news on public opinion over time are not, however, merely tem-
porary. Our findings support a theory of attitude change that is persistent after a single
exposure to partisan news media. After a week, the decay in the size of the persuasion effects
we identify is only minimal. Partisan media’s effects are not simply a short-term artifact of
the survey experimental environment, but instead have important implications for politics
and policy. The fact that the duration of persuasion is at least a full week after one instance
of experimental exposure to partisan news suggests that the media can have durable effects
on public opinion that subsequently may influence policy.
While our results contribute to a broader understanding of the relevance of media ef-
fects for democracy, they also point to several areas open for future research. For instance,
researchers should examine not just whether or not media effects decay over time, but deter-
25
mine the conditions under which these effects are more or less durable (e.g. Coppock, 2017).
In addition, the dynamic impact of partisan media on people’s behavior in the real-world
deserves greater attention. Understanding both the long-term effects of media on people’s
attitudes and their behavior can help produce a more comprehensive view of partisan media’s
role in individuals’ lives and democracy.
26
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31
Supplementary Appendix for
“Dynamic Persuasion: Decay and Accumulation of the
Persuasive Effects of Partisan Media”
A Main Persuasion Effects by Stated Preferences
A.1 Immediate Effects, Pooled
We first pool across the forced choice groups in waves 1 and 2 to assess the immediate effectsof partisan media. These effects are described in the main text, but also presented here inTable A1.
Table A1: Media Persuasion Effects by Respondent Stated Preference
Dependent variable:
attitudinal IndexForced Free No Controls Free Demographics
(1) (2) (3)
Entertainment 0.017 0.021 0.051∗
(0.013) (0.017) (0.029)
Fox 0.032∗∗∗ 0.067∗∗∗ 0.153∗∗∗
(0.012) (0.020) (0.046)
Prefer Entertainment 0.054∗∗∗ 0.094∗∗∗ 0.108∗∗
(0.012) (0.019) (0.045)
Prefer Fox 0.132∗∗∗ 0.139∗∗∗ 0.140∗∗∗
(0.012) (0.019) (0.028)
Entertainment × Prefer Entertainment −0.009 −0.048∗ −0.078(0.018) (0.026) (0.055)
Fox × Prefer Entertainment −0.015 −0.063∗∗ −0.121∗
(0.018) (0.032) (0.067)
Entertainment × Prefer Fox −0.005 −0.027 −0.051(0.018) (0.029) (0.045)
Fox × Prefer Fox 0.007 −0.048∗ −0.125∗∗
(0.017) (0.027) (0.054)
Constant 0.288∗∗∗ 0.285∗∗∗ 0.277∗∗∗
(0.009) (0.006) (0.010)
Observations 5,169 5,220 5,120R2 0.068 0.082 0.088Adjusted R2 0.066 0.081 0.087Residual Std. Error 0.216 (df = 5160) 0.212 (df = 5211) 0.562 (df = 5111)
Note: ∗p<0.1; ∗∗p<0.05; ∗∗∗p<0.01Standard Errors Clustered by Respondent
A.2 Immediate Effects, Disaggregated into Wave 1 and Wave 2
When we disaggregate the immediate effects of partisan media into the two different waves,we see slightly different effects among entertainment-preferrers in the first wave than in thesecond wave.
A-1
Attitudinal Index Sharing index
PreferEntertainment
PreferFox
PreferMSNBC
PreferEntertainment
PreferFox
PreferMSNBC
-0.10
(Moreliberal)
-0.05
0.00
(Moreconservative)
0.05
-0.10
(Lesswillingnessto share)
-0.05
0.00
(Greaterwillingnessto share)
0.05
Tre
atm
ent
effe
ct o
f w
atch
ing
Fox
rat
her
than
MSN
BC
Figure A1: Persuasion Results, Wave 1
●
●
●
●
●
●
Attitudinal index W2 Sharing index W2
PreferEntertainment
PreferFox
PreferMSNBC
PreferEntertainment
PreferFox
PreferMSNBC
−0.15
(Moreliberal)
−0.10
−0.05
0.00
0.05
(Moreconservative)
0.10
−0.15
(Lesswillingnessto share)
−0.10
−0.05
0.00
0.05
(Greaterwillingnessto share)
0.10
Trea
tmen
t effe
ct o
f rea
ding
Fox
rat
her
than
MS
NB
C in
W2
Figure A2: Persuasion Results, Wave 2
A-2
B Persuasion Results Continuous Treatment
To examine the effects of persuasion in another way in order to gain statistical power relativeto models that were fully disaggregated, in this section we also fit a model that makes anassumption about the symmetrical effects of MSNBC and Fox News – that is, Fox Newshas an effect on attitudes that is the opposite of the effect due to MSNBC. Formally, thisassumption defines the causal effect of partisan media τ as:
τ =E(Attitudinal Index|Fox)− E(Attitudinal Index|Read Entertainment) = (5)
− (E(Attitudinal Index|MSNBC)− E(Attitudinal Index|Read Entertainment)) (6)
τ can therefore be estimated by defining a continuous treatment variable, D, that is 1 fortreatment with Fox News, −1 for treatment with MSNBC, and 0 for Entertainment andfitting the model:
Attitudinal Index = α + τD + ε (7)
By pooling in this manner and assuming symmetry in the effects of the two news outlets,we gain additional power to detect the accumulation of persuasion effects.
Table A2 presents results for the persuasive effects of partisan media using this continuoustreatment indicator. The columns of Table A2 correspond to the wave of data used for themodel. Columns 1 and 2 correspond to models run on data from waves 1 and 2, respectively,while column 3 shows the results from a model pooling over both waves.
These results suggest that partisan media has an effect on respondents’ attitudes ofapproximately 0.015 along the unit scale — in the more conservative direction for Fox, andin the more liberal direction for MSNBC. Compared with the previous results that did notassume symmetry of persuasion effects, the pooled model estimate of .015 is substantivelysimilar to the previous estimates of -.013 for treatment with MSNBC and .018 for treatmentwith Fox (both relative to entertainment). The F test suggests the model which assumessymmetric persuasive effects for Fox and MSNBC actually significantly improves model fitrelative to the model which does not. Similarly, the F-test also suggests that a model whichallows treatment effects to vary between waves does not improve model fit. This demonstratesthat the assumption of symmetric persuasive effects for Fox and MSNBC is plausible.
A-3
Table A2: Main Results with Continuous Treatment
Dependent variable:
Attitudinal IndexWave 1 Wave 2 Waves 1 and 2 Pooled
(1) (2) (3)
Media Treatment 0.017∗ 0.013∗ 0.015∗
(0.005) (0.006) (0.004)
Constant 0.369∗ 0.376∗ 0.372∗
(0.004) (0.005) (0.004)
Observations 3,073 2,096 5,169R2 0.004 0.002 0.003Adjusted R2 0.004 0.002 0.003Residual Std. Error 0.220 (df = 3071) 0.228 (df = 2094) 0.223 (df = 5167)
Note: ∗p<0.05Standard Errors Clustered by Respondent In Pooled Model
A-4
C Heterogeneity of Decay Effects by Wave
● ●
●●
●
●
Attitudinal index W2 Sharing index W2
PreferEntertainment
PreferFox
PreferMSNBC
PreferEntertainment
PreferFox
PreferMSNBC
−0.15
(Moreliberal)
−0.10
−0.05
0.00
0.05
(Moreconservative)
0.10
−0.15
(Lesswillingnessto share)
−0.10
−0.05
0.00
0.05
(Greaterwillingnessto share)
0.10
Trea
tmen
t effe
ct o
f rea
ding
Fox
rat
her
than
MS
NB
C in
W1
Figure A3: Persuasion of Wave 1 Treatment on Wave 2 Outcomes (Free Choice W2 only)
Attitudinal index W3
PreferEntertainment
PreferFox
PreferMSNBC
-0.15
(Moreliberal)
-0.10
-0.05
0.00
0.05
(Moreconservative)
0.10
Tre
atm
ent
effe
ct o
f rea
ding
Fox
rat
her
than
MSN
BC
in W
1
Figure A4: Persuasion of Wave 1 Treatment on Wave 3 Outcomes (Free Choice W2 only)
A-5
Attitudinal index W3
PreferEntertainment
PreferFox
PreferMSNBC
-0.15
(Moreliberal)
-0.10
-0.05
0.00
0.05
(Moreconservative)
0.10
Tre
atm
en
t e
ffe
ct
of
rea
din
gF
ox r
ath
er
tha
n M
SN
BC
in W
2
Figure A5: Persuasion of Wave 2 Treatment on Wave 3 Outcomes
A-6
Dependent variable:
Next Wave attitudinal IndexForced Free No Controls Free Demographics
(1) (2) (3)
Entertainment 0.015 0.053∗∗∗ 0.006(0.012) (0.012) (0.019)
Fox 0.034∗∗∗ 0.129∗∗∗ 0.022(0.012) (0.011) (0.018)
Wave 3 0.017 0.010 0.014(0.011) (0.010) (0.032)
Entertainment × Wave 3 −0.012 −0.014 −0.046(0.017) (0.015) (0.043)
Fox × Wave 3 −0.015 −0.005 0.015(0.017) (0.014) (0.043)
Constant 0.359∗∗∗ 0.309∗∗∗ 0.366∗∗∗
(0.008) (0.008) (0.014)
Observations 4,156 4,092 4,066R2 0.003 0.057 0.018Adjusted R2 0.002 0.056 0.017Residual Std. Error 0.228 (df = 4150) 0.219 (df = 4086) 0.617 (df = 4060)
Note: ∗p<0.1; ∗∗p<0.05; ∗∗∗p<0.01Standard Errors Clustered by Respondent
A-7
D Cumulative Effects
Table A3: Cumulative Effects of Media Exposure
Dependent variable:
W2 Marijuana IndexForced Choice No Controls Free Choice Free Demographics
(1) (2) (3)
Fox At Least Once 0.008 0.071∗ 0.065∗
(0.026) (0.030) (0.023)
Entertainment At Least Once −0.013 0.055∗ 0.052∗
(0.026) (0.028) (0.024)
MSNBC Once −0.037 −0.028 −0.040(0.034) (0.043) (0.030)
Fox Twice −0.026 0.085∗ 0.085∗
(0.038) (0.036) (0.031)
Entertainment Twice −0.008 −0.006 −0.019(0.036) (0.039) (0.033)
Constant 0.408∗ 0.311∗ 0.321∗
(0.049) (0.050) (0.045)
Observations 1,044 1,065 1,061R2 0.005 0.100 0.086Adjusted R2 −0.0002 0.096 0.082Residual Std. Error 0.233 (df = 1038) 0.214 (df = 1059) 0.295 (df = 1055)F Statistic 0.968 (df = 5; 1038) 23.619∗ (df = 5; 1059) 19.904∗ (df = 5; 1055)
Note: ∗p<0.05
A-8