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RESEARCH ARTICLE
Walking the walk? Experiments on the effect
of pledging to vote on youth turnout
Mia Costa
1¤
*, Brian F. Schaffner
1
, Alicia Prevost
2
1Department of Political Science, University of Massachusetts Amherst, Amherst, MA, United States of
America, 2Environmental Defense Fund, Washington, DC, United States of America
¤Current address: Department of Government, Dartmouth College, Hanover, NH, United States of America
*mia.costa@dartmouth.edu
Abstract
Psychological theories of political behavior suggest that commitments to perform a certain
action can significantly increase the likelihood of such action, but this has rarely been tested
in an experimental context. Does pledging to vote increase turnout? In cooperation with the
Environmental Defense Fund during the 2016 election, we conduct the first randomized con-
trolled trials testing whether young people who pledge to vote are more likely to turn out than
those who are contacted using standard Get-Out-the-Vote materials. Overall, pledging to
vote increased voter turnout by 3.7 points among all subjects and 5.6 points for people who
had never voted before. These findings lend support for theories of commitment and have
practical implications for mobilization efforts aimed at expanding the electorate.
Introduction
Voting is one of the most important civic opportunities offered to citizens, yet the persistent
low participation rates of young people have long puzzled scholars, policymakers, and activists
concerned with cultivating an active electorate. Ever since 18-year-olds were first given the
right to vote in 1972, the youth vote has consistently lagged behind that of older generations.
In 1972, 51% of 18-to 24-year-olds voted compared to 70% of people who were 25-years-old
and older. The age gap in voter turnout was not much better in 2016, with turnout levels at
50% for young people and 65% for those above 25 years old [1]. Young citizens may vote at
lower rates than other Americans for a variety of reasons. Young people have fewer resources
that are traditionally thought to increase one’s participation, such as education and income
[2]. The informational costs of finding out how and where to register to vote and cast one’s bal-
lot can deter participation for some newly eligible voters [3,4]. Indeed, there is some evidence
that suggests allowing young citizens to register to vote before they are actually eligible—thus
diminishing their chances of missing registration deadlines—can increase youth turnout [5].
Moreover, the lack of geographic stability of many young people poses additional costs for
voter registration and turnout [6].
Political scientists have long argued that mobilization is a key factor in getting people to
turnout to vote. Recent studies using field experiments have shown how effective grassroots
tactics can be in mobilizing people to vote [7,8], but turnout among young citizens has not
PLOS ONE | https://doi.org/10.1371/journal.pone.0197066 May 29, 2018 1 / 16
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Citation: Costa M, Schaffner BF, Prevost A (2018)
Walking the walk? Experiments on the effect of
pledging to vote on youth turnout. PLoS ONE 13
(5): e0197066. https://doi.org/10.1371/journal.
pone.0197066
Editor: John Holbein, Brigham Young University,
UNITED STATES
Received: August 28, 2017
Accepted: April 25, 2018
Published: May 29, 2018
Copyright: ©2018 Costa et al. This is an open
access article distributed under the terms of the
Creative Commons Attribution License, which
permits unrestricted use, distribution, and
reproduction in any medium, provided the original
author and source are credited.
Data Availability Statement: All relevant data
underlying the results of the study have been
uploaded to the Harvard Dataverse and are
accessible using the following link: https://doi.org/
10.7910/DVN/UTX95J.
Funding: Partial funding for the Pennsylvania
experiment came from The Pluribus Project (http://
www.pluribusproject.org/). The Pluribus Project
had no role in study design, data collection and
analysis, decision to publish, or preparation of the
manuscript. Environmental Defense Fund provided
the remaining funds for implementing the
been widely studied. Few mobilization campaigns focus specifically on young people, in part
because of the low returns anticipated with targeting America’s least active portion of the elec-
torate. One technique that has become more common in campaigns’ repertoire of mobiliza-
tion techniques, especially to boost youth voter turnout [9], is the use of vote pledges. The
intuition behind this mobilization tactic is simple: if a person commits to a future behavior,
they will be more likely to follow through on that behavior than someone who was not asked
to commit.
Does committing to participate increase political engagement? Specifically, we are inter-
ested in whether pledging to vote increases the likelihood that an individual will turn out to
vote. Research on cognitive psychology suggests that commitments to perform a certain action
can significantly increase the likelihood of such action, but this has rarely been empirically
tested in a political context. While pledging is a relatively simple mobilization tactic, it invokes
basic psychological processes above and beyond the traditional demographic parameters in
models of voter turnout, such as education, race, and age [10]. Theories of commitment, cog-
nitive dissonance, and self-perception suggest that pledging to vote may engage a whole host
of psychological mechanisms that explain how individuals can be persuaded by their own
actions.
In cooperation with the Environmental Defense Fund (EDF), first during the 2016 Pennsyl-
vania primary election and second during the general election campaign in Colorado, we con-
duct the first randomized controlled trials testing whether individuals who pledge to vote are
more likely to turn out than individuals who are contacted using standard Get-Out-the-Vote
(GOTV) materials, such as reminders and information about the election. Overall, we find
that pledging to vote had a significant impact on turnout among individuals who had not pre-
viously voted. The Pledge to Vote campaign was particularly effective for bringing new voters
into the electorate in large numbers, rather than just ensuring turnout among regular voters.
These findings suggest that new voters are more susceptible to commitments to participate in
politics and have practical implications for increasing youth turnout.
The psychological bases of voting behavior
Several different psychological theories of behavior suggest that “talking the talk” can lead indi-
viduals to “walk the walk.” Applying these theories to voter turnout critically hinges on con-
ceiving of voting as a dynamic set of behaviors that extend over time, rather than one static act
[11]. Events that occur before a person decides to vote, including processes of cognition, can
influence whether or not they follow through and actually cast a vote. Our particular prebeha-
viorial theory of voting departs from the view that voting serves an instrumental, electoral
function for quasi-rational individuals (i.e. that their individual vote will affect the election
outcome), and instead treats voting as a cognitive process and an act of self-expression.
First, theories of self-prediction suggest that if people expressly predict that they will behave
a certain way, then they are more likely to follow through on that behavior. This phenomenon
is described in different literatures as the “self-erasing nature of errors of prediction” [12], the
“self-prophecy effect” [13], and the “mere measurement effect” [14]. Applied to a GOTV con-
text, the expectation is clear: a person is more likely to vote if they had previously predicted that
they would do so. The most recent empirical evidence on the effectiveness of voting self-pre-
dictions, however, is more mixed. In an analysis of an experiment conducted during the 2000
presidential primary, Smith, Gerber, and Orlich [15] find that neither being asked to predict
whether one would vote or to provide an “important reason” for voting increased one’s likeli-
hood of turning out to vote. Nickerson and Rogers [16] additionally find that during the 2008
Pennsylvania primary, self-predictions had a statistically significant but weak effect on turnout.
Experiments on the effect of pledging to vote on youth turnout
PLOS ONE | https://doi.org/10.1371/journal.pone.0197066 May 29, 2018 2 / 16
experiments and was involved in designing the
pledge materials used in the experiments and data
collection. The Environmental Defense Fund had no
role in data analysis, decision to publish, or
preparation of the manuscript. There was no
additional external funding received for this study.
Competing interests: The authors have declared
that no competing interests exist.
Combining the self-prediction ask with a voting implementation plan was more effective; that
is, individuals who were asked to predict whether they would vote and also to answer a series
of questions regarding their plan on election day (i.e. what time they will vote, where they will
be coming from, etc.) were significantly more likely to turnout to vote than those who were
only asked to predict whether or not they would vote.
One reason why voting plans are more effective than self-predictions alone is because ver-
balizing implementation intentions mimics a sort of commitment. There is a long-standing
body of literature that suggests individuals will stick to a previous commitment—especially if
they receive a reminder of that commitment—in order to avoid feelings of inconsistency and
cognitive dissonance between their expressed intentions and behavior [17–20]. Cognitive dis-
sonance is foundationally described as a mental state that occurs in the context of a “belief
dilemma”: the uncomfortable psychological conflict between two or more beliefs [17]. Applied
to an action-based model, cognitive dissonance can influence people to act in a certain way
that accords to their attitudes [21,22]. When actions do not match cognition, dissonance
occurs.
Self-perception theory developed in contradiction to theories of cognitive dissonance, yet
both are related in explaining one’s propensity to follow through on a prior commitment.
Self-perception theory suggests that attitudes are induced from behavior, rather than the
other way around [23,24]. Individuals develop and establish their attitudes by observing
their actions and inferring what attitudes must have led to those actions. Therefore, initial
commitments can change an individual’s self-image, thereby promoting later behaviors that
align with that self-image. Appealing to this behavioral pattern is known as the foot-in-the-
door technique [20,25]. Once an individual complies with an initial request (i.e. signing a
pledge to vote card), they will be more likely to comply with a subsequent, larger request
(i.e. voting). This is in contrast to the door-in-the-face technique [26], where someone first
rejects an initial request that is too extreme, resulting in feelings of obligation that cause
them to agree to a second, smaller request. Notably, McCabe and Michelson [27] test how
effective this technique is in turning people out to vote and find that simply asking people if
they could be counted on to vote is much more effective. Additional evidence suggests that
follow-ups and reminders of one’s prior behavior can significantly increase the likelihood of
subsequent action [28,29].
Indeed, explicitly committing to a particular way of acting adds a public element to one’s
perceived sense of self. In this sense, self-perceptions not only internally drive people to act a
certain way, but can also increase the perceived social costs of failing to fulfill that self-percep-
tion [30]. Commitments activate a basic psychological desire in people to behave in manner
that is consistent with both their own self-perceptions and the social norms attributed to those
perceptions [23,24,30]. Pledging to vote, for example, may invoke self-perceptions of oneself
as a “voter.” Social identity theories suggest that a person’s self-esteem increases when they
behave in ways that are consistent with the behavior of in-groups with which they identify
[31], and this pattern becomes stronger as the norm of voting becomes more salient in one’s
social network [32]. Therefore, being reminded of one’s pledge to vote may contribute to a per-
son’s identity as a voter and the accompanied social norm that voting is important.
One example of the power of pledges to invoke dissonance is the myriad of behaviors indi-
viduals have been found to engage in to maintain consistency. Not only do people express
attitudes that accord with their behaviors [23], but if a behavior is inconsistent with prior atti-
tudes and commitments, people may alter their perceptions about the prior behavior. For
example, in a longitudinal study of middle- and high-schoolers, 82% of those who pledged
abstinence but then engaged in sexual activity denied ever having taken a pledge of abstinence
in the first place [33].
Experiments on the effect of pledging to vote on youth turnout
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We therefore expect people who pledge to vote to be more likely to turn out because they
observe and recall their act of pledging, and thus infer that voting is an important element of
their self-image and identity. It is this self-induced attitude about the importance of voting
that would then lead to cognitive dissonance if the commitment to vote was not adhered to.
Therefore, we posit that both self-perception and cognitive strategies to avoid dissonance
would lead people who pledge to vote to turn out to vote on election day.
However, we expect that there will be differential effects among people who vote regularly,
people who regularly do not vote, and people who are “on the cusp of voting” [34,12] such as
young adults. Specifically, we expect that those in that latter category should be more suscepti-
ble to the theories of self-perception and cognitive dissonance outlined above. Behaviors are
most likely to translate into attitudes when attitudes about the behavior have yet to be fully
crystallized [23]. Therefore, if pledging does invoke self-perceptions about voting, the effects of
the pledge campaign should be the most pronounced for people who have not yet created an
identity around the act of voting. People who have not experienced the cognitive process of
identifying as a voter, non-voter, or occasional voter, are the ones that have the most to “gain”
(i.e. are the most likely to see a change in their behavior).
Notably, young adults become eligible to vote at the same time that they are particularly
“vulnerable” to attitudinal change. The impressionable years hypothesis asserts that young
people are more open to persuasion when it comes to attitudes and behaviors in part because
they are in the midst of forming a self-identity and establishing the behaviors associated with
that identity [35,36]. For these reasons, young adults are a group who may be especially influ-
enced by pledging to vote, and the impact of such effects may persist over the long term. After
all, the habitual voting literature argues that once an individual votes it is likely that she will
turn out to vote in subsequent elections [37–41]. Thus, the earlier that eligible voters get to the
polls, the more likely that we will see higher levels of general participation. This suggests that
young people are not only an especially persuadable group of voters, but they are also a group
for which a single act of mobilization can spur a lifetime of turnout.
Despite the rich theoretical body of literature that suggests pledging can increase the likeli-
hood of a behavior, surprisingly little has been done to empirically test this theory, especially
in political contexts. Much of the research on the power of pledges to impact behavior has
studied non-political outcomes. For example, individuals who pledge to recycle have been
found to be significantly more likely to do so than individuals who did not pledge to recycle
[42]. Similar effects have been found for wearing seat belts [43] and safety glasses [44]. These
studies, however, are relatively under-powered and future research is needed to better under-
stand the effect of pledging on these behaviors.
One study analyzed data from a 1996 Rock the Vote campaign that used pledge reminders
to increase voter turnout [9]. However, there are three limitations to the ability to draw strong
causal inferences from this study. First, the authors did not investigate whether pledges
increased turnout over other GOTV tactics, such as simply encouraging people to vote and
providing information about the election, but rather whether a personalized pledge was more
effective than a generic pledge. Second, the study was not a randomized controlled trial but
rather an analysis of observational data. Third, the authors rely on self-reported measures of
turnout for their outcome variable instead of using validated vote records. Our study seeks to
extend and improve upon this work by implementing two randomized controlled trials to
examine the effect of pledging on turnout in comparison to traditional GOTV tactics. By
administering pledges randomly, we can draw out clear causal effects of the campaign. Addi-
tionally, by using validated voter turnout, we avoid the limitations of self-reported turnout—
specifically, the tendency of individuals to lie about voting.
Experiments on the effect of pledging to vote on youth turnout
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Experimental design
Human subject research approval came from the University of Massachusetts Amherst
Human Research Protection Office, Protocol ID 2017-3629. The Pledge to Vote campaigns
in both Pennsylvania and Colorado were designed to determine whether having individuals
pledge to be a voter in an upcoming election would make them more likely to vote compared
to traditional mobilization techniques, such as reminders and encouragement to turn out.
Note that our control is not a “true control” group of people who were not contacted at all.
Rather, we are comparing the effectiveness of the pledge compared to a petition among people
who were contacted. This is akin to an A/B test and follows the approach of many randomized
controlled trials where the point of interest is the effectiveness of various interventions in
comparison to one another [45,46]. Working with Defend Our Future (DOF), a campaign of
Environmental Defense Fund (EDF), we designed a field experiment to measure the effective-
ness of a pledge to vote program that Defend Our Future was already planning to run in Penn-
sylvania and Colorado. These states were chosen by DOF because a) they were swing states
particularly important to the election, and b) implementation was aided by DOF’s grassroots
operations already on the ground in those areas. Given the nature of the organization, the cam-
paign was focused around a message involving climate change.
Study 1: Pennsylvania
During March and April of 2016, DOF staff recruited individuals on five college campuses in
the Philadelphia area (Drexel University, University of Pennsylvania, St. Joseph’s University,
Temple University, and Villanova University). These particular campuses were ideal for our
purposes because they varied in terms of the student population size and demographics. For
example, Temple University is a relatively racially diverse public university with over 36,000
undergraduate students, whereas St. Joe’s is a mostly white, private Jesuit university of less
than 9,000 undergraduate students.
The Pennsylvania mobilization effort was strictly nonpartisan—DOF did not support any
candidate in the elections. All of the funding for the effort was tax deductible (501c3), which,
by regulation, could not be used for partisan political activity. The nonpartisan identity of this
campaign enabled us to examine the effect of pledging absent any partisan cues. It also posi-
tioned DOF as an alternative to hyper-partisan independent expenditure groups who were
already on the ground in Pennsylvania.
DOF had a team of more than a dozen people in Pennsylvania that included a field director,
field organizers, volunteers, and interns. The pledge to vote program was an extension of the
grassroots organizing work that the DOF organizing team had been conducting on Pennsylva-
nia campuses since the beginning of the 2015-16 school year. For the experiment, DOF orga-
nizers recruited individuals to participate through a variety of campus-based communications
including: canvassing in high-traffic areas on campuses, presenting in front of classes, reaching
out to student groups and clubs, and hosting on-campus social events.
The recruitments happened in 93 shifts of approximately 4 hours each across the course of
more than one month. We randomly assigned each shift so that all individuals contacted dur-
ing a particular shift would either be asked to sign a petition form indicating they would like to
be reminded about the election or to sign a pledge to vote. On both cards, individuals filled out
their name, address, and contact information. Both the petition (control) cards and pledge
(treatment) cards are shown in S1 Fig. In total, 4,110 individuals received the “pledge to vote”
contact and 1,655 received the generic turnout contact, where they simply received informa-
tion about the election. This imbalance was by design; DOF believed that the pledge to vote
appeal would be more effective and thus we worked with them to minimize the size of the
Experiments on the effect of pledging to vote on youth turnout
PLOS ONE | https://doi.org/10.1371/journal.pone.0197066 May 29, 2018 5 / 16
control group. Thus, we assigned shifts to the control condition with a probability of 0.3 and
to the pledge treatment with a probability of 0.7.
All individuals who were contacted were sent a reminder to vote in the mail during the
two weeks before the election. Individuals who pledged to vote were sent their pledge while
those who signed the petition simply received a generic message encouraging them to vote:
“Remember to vote in Pennsylvania’s primary on April 26, 2016.” The pledge card reminder,
in contrast, specifically reminded subjects of their pledge: “Remember your pledge to vote in
Pennsylvania’s primary on April 26, 2016.”
Fig 1 shows the number of individuals recruited for each day of the campaign in Pennsylva-
nia. One important feature of this program was that for circumstances beyond our control,
most of our recruitments happened after the March 28th deadline by which individuals had to
register in order to participate in the primary election on April 26th. This clearly did not pre-
clude the organizers from contacting large numbers of individuals, but it did mean that if an
individual was not already registered to vote they would not be able to participate in the April
26th primary election.
Field organizers entered contact information for individuals into the Voter Activation Net-
work and we then matched this list to the Catalist database. Catalist is a voter file firm that con-
tains individual-level data on over 240 million voting-age individuals. In Pennsylvania, we
were able to successfully match 55% of the records to an individual with an address in Pennsyl-
vania in the Catalist database. Since it is highly likely that someone who was unable to be
matched to the voter file is registered to vote, any individual who was unmatched was consid-
ered to be a non-voter. This follows the approach recommended by Ansolabehere and Hersh
[47] (see also [48]). In addition, our analysis focuses on individuals who could have actually
voted as a result of the treatment. This includes all individuals who were contacted before the
Fig 1. Number of contacts in Pennsylvania.
https://doi.org/10.1371/journal.pone.0197066.g001
Experiments on the effect of pledging to vote on youth turnout
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March 28th registration deadline and anyone contacted after the deadline who had registered
to vote before the deadline (thereby making them eligible to participate in the primary).
The nature of the campaign in Pennsylvania is important to consider when examining the
effectiveness of vote pledges. In general, turnout in primary elections is significantly lower
than in general elections. In 2016, about 33.7% of eligible voters participated in the Pennsylva-
nia primary. In addition, while the Democratic nomination for president was still being con-
tested at the time of the Pennsylvania primary, all challengers to Donald Trump had already
withdrawn from the Republican contest. Both of these contextual factors make the Pennsylva-
nia primary election a particularly difficult case for increasing turnout.
Study 2: Colorado
The second experiment took place during the general election campaign in the state of Colo-
rado. DOF had organizers on the Auraria Campus in Denver where Auraria Community Col-
lege, Metropolitan State University of Denver, and the University of Colorado Denver all share
a campus. They also canvassed on Colorado State University’s campus in Fort Collins and at
the University of Colorado campus in Boulder. As was the case in Pennsylvania, organizers
recruited individuals by canvassing in high-traffic areas, presenting in front of classes, reaching
out to student groups and clubs, and hosting on-campus social events. Shifts in Colorado were
randomized in the same manner as those in Pennsylvania—91 shifts (71%) were randomly
assigned to the pledge condition while 37 were assigned to the control condition. As with the
Pennsylvania experiment, the imbalance in the assignment of shifts to the control and treat-
ment groups was by design.
In total, the organizers recruited 6,176 individuals from September 26 through November
2, 2016: 4,340 pledge to vote cards (70.3%) and 1,836 petition signatures (29.7%). The pledge
and petition materials for this study were similar to the ones used in Pennsylvania (See the
Supporting Information for images of the treatment and control cards).
There are several advantages to conducting a second experiment, especially in Colorado.
First, turnout should not be unequal in a general election swing state along partisan lines, like
it may have been in Pennsylvania given the uncontested Republican presidential primary. Sec-
ond, understanding the effects of pledging to vote in both a primary and general election adds
important information about whether this strategy can be applied to different types of elec-
tions. In particular, is the pledge to vote tactic more effective in primaries than in more salient
general election campaigns?
Third, unlike Pennsylvania, Colorado allows citizens to register to vote up to and on the
day of the election. Thus, mobilization efforts that happened closer to the date of the election
could still be fully effective, unlike in Pennsylvania where only registered citizens could be
mobilized after the registration cut-off date. We therefore include everyone who was contacted
by DOF in the analysis.
Who was recruited?
Before analyzing how pledges influenced turnout, we first elaborate on the demographic pro-
file of individuals who were reached by the organizers. Table 1 shows the composition of these
individuals in terms of the percentage successfully matched to the voter file and, among that
group, their age, gender, race, partisanship, and vote likelihood. The pledge group and the con-
trol group are remarkably balanced. Of particular importance is the average score of recruits
on the vote propensity models. These models are created by voter file firms to predict how
likely they think an individual is to vote on a score of 0 to 100. In Pennsylvania, the average
score for members of the control group was 59.8 while those in the treatment group received
Experiments on the effect of pledging to vote on youth turnout
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an average score of 59.2. The average scores were similarly close in Colorado, with an average
of 68.3 for the control group and 69.7 for those recruited to sign a pledge to vote.
Both the pledge program and petition program appeared to be particularly effective in
reaching DOF’s target audience of young individuals. The average age among those recruited
in Pennsylvania was 24, and the median age was 21. In other words, more than half of those
recruited were 21 or younger. For many, this was the first election for which they had been
eligible to vote. Likewise, the median age of individuals recruited in Colorado was 20 for the
pledge group and 21 for the control group. While the canvassers were located on college cam-
puses to mostly recruit young adults, some people who were contacted were not students.
About 12% of the subjects in Pennsylvania for whom we have age information from the voter
file were 30 years of age or older. In Colorado, about 8% were 30 or older. In S2 Table, we
show that the treatment effects are robust to limiting our analysis to young adults.
Accounting for shift randomization
As noted above, the nature of the mobilization campaign run by DOF precluded us from con-
ducting individual-level assignment to the treatment and control conditions. Instead, random-
ization was conducted at the shift level. Accordingly, we need to be attentive to that fact as we
analyze the results. Fortunately, DOF’s organizers kept track of the shifts during which each
individual was contacted, as well as the canvasser who contacted each individual. In analyzing
the results in the following sections, we use cluster robust standard errors to account for clus-
tering by shift. Additionally, in the Supporting Information, we add an analysis in which we
control for the canvasser who recruited each individual. We do this to ensure that our results
are not a by-product of the particular canvasser who was assigned to each shift. Our findings
are robust to this alternative specification.
Finally, an additional concern might be that some individuals would be more likely to sign
a petition than a pledge (or vice versa) and that this propensity may be related to their likeli-
hood of voting. While we cannot absolutely rule out this possibility, there are several reasons
to think that this is not likely to be a concern. First, during the recruitment, individuals who
were approached were only aware of the type of form they were signing well after they began
the conversation with the organizer. Thus, by design, there would be no reason to expect that
people contacted in one condition would be less likely to at least begin a conversation with an
organizer than they would in the other condition. Second, the rate of successful recruitments
Table 1. Demographic profile of contacts.
Type % Matched Median Age % Female % White Avg. Partisanship Avg. Vote Likelihood
Study 1: PA
Pledge Group 54% 20 62% 75% 70.6 59.2
N = 4,110
Control Group 56% 21 61% 74% 72.5 59.8
N = 1,655
Study 2: CO
Pledge Group 74% 20 61% 84% 64.6 69.7
N = 4,294
Control Group 77% 21 57% 84% 61.8 68.3
N = 1,783
Note: Table presents the demographic comparison of contacts in the pledge (treatment) and petition (control) groups for both studies. Data on these measures is
available only for individuals successfully matched to Catalist.
https://doi.org/10.1371/journal.pone.0197066.t001
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made during pledge versus petition shifts were almost perfectly in line with what we would
expect given how many shifts were assigned to each condition. For example, in Pennsylvania,
69.9% of shifts were assigned to the pledge condition and 71.3% of our subjects signed a pledge
to vote. In Colorado, 71.1% of shifts were assigned to the pledge condition and 70.6% of indi-
viduals recruited were in the pledge condition. Thus, it does not appear to be the case that one
type of shift resulted in higher recruitment rates than the other. These patterns, in conjunction
with the balance comparison presented above, help to bolster the expectation that the control
and treatment groups were equivalent except with regard to the type of commitment obtained
from the subject.
Results: Study 1
To determine the effectiveness of the pledge campaign, it is necessary to compare individuals
who signed a petition (the control group) with those who signed a pledge (the treatment group).
Table 2 shows several different treatment effects. The first line in the table simply includes
every individual who was contacted by DOF. Among the full set of contacts, turnout was quite
low and the small difference between the treatment and control groups was in the opposite
direction than hypothesized. However, recall that this comparison includes a large number of
individuals who could not have been affected by the treatment even if it was persuasive. This is
the case because anyone who was contacted after the registration deadline of March 28th was
ineligible to vote in the primary unless they had already registered to vote in Pennsylvania.
Accordingly, the second line in the table restricts our comparison to only those individuals
who could have actually voted as a result of the treatment. This means that we include all indi-
viduals who were contacted before the March 28th registration deadline, as anyone contacted
before the deadline could have registered in time to vote in the primary. For those contacted
by DOF after the registration deadline, we restrict the subject pool only to those who were
already registered to vote. We do this since one could not be affected by the treatment if they
were not registered to vote by that date.
The second set of results in Table 2 (“All eligible individuals”) shows the comparison of
turnout between those who received the standard mobilization contact and those who were
asked to sign a pledge to vote. Among these individuals who could actually have been affected
by the contact, people who signed the pledge had a 4.5 percentage point higher chance of vot-
ing in the primary than those who signed a petition. Note that the standard errors and p-values
in all our analyses are calculated using cluster robust standard errors to account for clustering
by the shift during which an individual was recruited.
Table 2. Effect of treatment and control on voter turnout—Pennsylvania primary.
Group Control Group Pledgers Difference
All individuals contacted 15.7% 15.1% -0.6%
(1.4) (0.1) p = 0.721
N = 1,655 N = 4,110
All eligible individuals 34.6% 39.1% +4.5%
(3.3) (2.0) p = 0.199
N = 751 N = 1,589
Never voted previously 28.4% 37.2% +8.8%
(4.3) (3.1) p = 0.057
N = 457 N = 924
Note: Cluster robust standard errors (in parentheses) adjust for clustering by recruitment shift.
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Of course, the pledge campaign is specifically designed to mobilize individuals who have
not previously participated in the electoral process. Thus, the third line of results in the table
shows the same turnout comparison, but only for those who had not previously voted. We
defined previous non-voters as anyone for whom there was no valid vote record in 2014, 2012,
or 2010 (which includes people for whom there were no registration records at all). Among
that group, the pledge appears to be more effective. First time voters who signed the pledge
turned out at a rate that was 8.8 percentage points higher than first time voters who received
the standard mobilization message. The treatment effect among individuals who had voted
previously was actually—2.4 points (p = 0.533). In a simple OLS model, an interaction term
for previous non-voters and the pledge treatment produces an estimated interaction effect of
11.2 points, with p = 0.058.
Results: Study 2
The Colorado experiment offered an opportunity to examine our treatment effects on a larger
scale and in a competitive swing state during the general election. It also removed many of the
complications created by the registration deadline in Pennsylvania since Colorado residents
can register to vote up to and on the day of the general election. Thus, if an individual was con-
tacted by DOF and provided a Colorado address, then whether they were presently registered
or not was not an impediment to them being affected by that recruitment. Accordingly, we
include in our analysis everyone who was contacted by DOF, regardless of whether they were
matched to the Catalist database. This approach allows us to avoid the concerns about post-
treatment bias described by Nyhan et. al. [49].
Table 3 shows the treatment effects for our Colorado study. We show three sets of results.
The first line includes in the subject pool every individual contacted by DOF during the cam-
paign, even if they provided an address outside of the state of Colorado. Of the 1,841 individu-
als who were recruited by DOF to sign a petition, 60.8% were matched to a validated vote
record in the state of Colorado. By comparison, of the 4,374 individuals DOF recruited for
the pledge to vote condition, 65.0% were matched to a valid record of turnout in Colorado in
November 2016. This amounts to a 4.2 percentage point increase in the turnout rate among
individuals in the pledge to vote group (p = 0.007).
A small number of individuals who were contacted in Colorado by DOF provided a home
address outside of the state of Colorado. Accordingly, the second set of results in Table 3 limits
our analysis to individuals who provided an address in the state of Colorado. Among this
group we find a relatively similar treatment effect of 3.5 percentage points (p = 0.020).
Table 3. Effect of treatment and control on voter turnout—Colorado general election.
Group Control Group Pledgers Difference
All individuals contacted 60.8% 65.0% +4.2%
(1.4) (0.7) p = 0.007
N = 1,841 N = 4,374
All individuals with CO address 62.6% 66.2% +3.5%
(1.3) (0.8) p = 0.020
N = 1,783 N = 4,294
CO address & never voted previously 52.0% 57.0% +5.0%
(1.8) (0.9) p = 0.015
N = 1,319 N = 3,212
Note: Cluster robust standard errors (in parentheses) adjust for clustering by recruitment shift.
https://doi.org/10.1371/journal.pone.0197066.t003
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Finally, the third set of results in Table 3 focuses on individuals who were likely to have
not been previous voters. Our group of previous non-voters includes anyone who was not
matched to a record in Catalist as well as those who were matched but for whom we could find
no record of turnout in 2016, 2014, 2012, or 2010. We identify unmatched individuals as previ-
ous non-voters because the fact that we were unable to find a record for them in Catalist (espe-
cially combined with their young age) is likely the result of the fact that they have never been
registered to vote. Note that reducing the analysis to previous non-voters only leads to a rela-
tively small reduction in the sample size; this is due to the fact that by focusing the mobilization
campaign on young adults, we are already focused on a population that had mostly not voted
before. The effect of the pledge treatment was higher among this group—5 percentage points.
The treatment effect among individuals who had voted previously was just 0.6 percentage
points (p = 0.650). In a simple OLS model, an interaction term for previous non-voters and
the pledge treatment produces an estimated interaction effect of 4.3 points, with p = 0.070.
Combined effect from both studies
Given the similarity of the two experiments we carried out in 2016, it is possible to conduct a
simple meta-analysis to estimate the combined effect of the pledge to vote treatments across
both studies. The meta-analysis approach gives more weight to studies that measure the treat-
ment effect with more precision; thus, in meta-analyzing the Pennsylvania and Colorado
experiments, the Colorado study is given about four-times as much weight as the Pennsylvania
experiment due to the much larger usable subject size. Fig 2 plots the results from a fixed
effects model for all subjects and for previous non-voters. Note that the results are the same
using a random effects model.
Fig 2. Meta-analysis showing combined treatment effect in both studies.
https://doi.org/10.1371/journal.pone.0197066.g002
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For all subjects across the two experiments, the effect of signing a pledge to vote rather
than a traditional petition was 3.7 points, with a 95% confidence interval ranging from 1 to 6.4
points. For previous non-voters the estimated effect is somewhat larger—5.6 points, with a
confidence interval ranging from 1.9 to 9.2 points.
How do these treatment effects compare to other field experiments that test the effects of
particular types of messaging on turnout? Green, McGrath, and Aranow [50] summarize the
research on message effects in mobilization field experiments. They conclude that “arguments
used to encourage voting (civic duty, the closeness of the race, group solidarity) tend to have
relatively minor effects, whereas the norms used to frame those arguments (e.g., social pres-
sure, gratitude) have much stronger effects.” As an example of the latter (stronger) effects, Ger-
ber, Green, and Larimer [45] find that individuals exposed to a message that is designed to
heighten the social pressure to vote are up to 6.3 points more likely to vote than those who
were exposed to a simple “civic duty” message. Other field experiments testing a social pres-
sure message have shown similarly large effects relative to a more basic civic duty message
[51]. Thus, our “pledge to vote” intervention appears to have a somewhat more modest
sized mobilization effect than has been found for social pressure mailers, though the pledge
treatment can be administered without concerns about negative backlash that have been
cited for social pressure messaging [52]. In addition, changing from one GOTV message to
another (such as a pledge) is effectively costless, so this intervention should not be difficult to
implement.
Discussion
This research contributes to a growing body of work that uses field experiments to understand
voter behavior. In this paper, we provide evidence that having individuals pledge to vote is an
effective way to increase turnout. This is especially true for individuals who have not previ-
ously participated in the political process, such as young adults. From a practical standpoint,
this simple mobilization tactic could stimulate increased voter turnout among a relatively inac-
tive segment of the eligible electorate, especially considering the cost to implement a pledge
campaign is about the same as any other GOTV campaign. If voting is a habitual behavior [37,
40], getting new voters to the polls could have substantial long-term effects on overall voter
turnout.
Our study is a first step at exploring the effect of pledging to vote on turnout. We designed
the experiments under a variety of constraints and more experiments should be conducted to
test the generalizability of our results to other contexts. For example, future studies should
examine the impact of pledges in settings other than college campuses with more diverse target
populations. There is also some reason to think that pledging effects may vary by racial or eth-
nic group since whites, African Americans, and Latinos (for example) all have different voting
patterns. Self-perceptions about voting might therefore be enhanced among certain groups,
creating lower thresholds for cognitive dissonance for reneging on a pledge to vote. While
DOF organizers were able to contact relatively high numbers of non-white individuals in
Pennsylvania, after constraining our analysis to those who were registered by the cut-off
date, there there were not enough non-whites to uncover statistically significant trends for the
effect of pledging to vote for racial or ethnic minorities. Future research should examine this
dynamic in more detail.
More research is also needed to examine the impact of vote pledges as utilized through a
campaign focused on different issue areas, or a non-issue campaign. The Environmental
Defense Fund’s focus on climate change may affect turnout rates because people may self-
select into recruitment based on their positions surrounding environmental policies. While
Experiments on the effect of pledging to vote on youth turnout
PLOS ONE | https://doi.org/10.1371/journal.pone.0197066 May 29, 2018 12 / 16
this self-selection should be random across our treatment and control groups, thus not biasing
the extent to which we can make causal estimates of the effect of the treatment, it would be
worthwhile to test whether pledges affect behavior absent their association to a particularized
message.
Additionally, research should examine different types of pledges. Personalized GOTV
appeals have been found to be more successful at mobilizing people to vote than non-personal-
ized appeals [7,9]. In addition, people are motivated to vote by those in their social networks
[32]. Therefore, are pledges that are personalized or appeal the social aspect of voting more
effective at increasing turnout than standard pledges? In a similar vein, are there spillover
effects of pledging among individuals in the same social network?
Finally, there are a series of unanswered questions regarding other potential outcomes of
pledges. Our study is limited to voter turnout, but it is possible that pledges can be used to
increase a whole host of other political behaviors. Does pledging make people more likely to
attend rallies, put up yard signs, influence others to vote, or write to one’s elected official?
Other downstream effects of pledging should also be considered. Does pledging to vote only
increase one’s likelihood to vote in the next election, or does a newfound ‘voter identity’ influ-
ence people to continue to participate in politics? We look forward to future experiments that
take on these questions.
Supporting information
S1 Fig. Study 1: Solicitation materials.
(TIFF)
S2 Fig. Study 1: Reminder cards.
(TIFF)
S3 Fig. Study 2: Solicitation materials.
(TIFF)
S4 Fig. Study 2: Reminder cards.
(TIFF)
S1 Table. Robustness of results when controlling for canvasser. Given that randomization
occurred at the shift stage, one concern would be that particular canvassers are “more effec-
tive” than others and that they might be assigned to a disproportionate number of pledge or
control shifts. If this were to occur, then the findings we report in the paper may actually result
from canvasser effectiveness rather than the treatment itself. Fortunately, DOF was able to sup-
ply us with the canvasser who contacted each subject in our experiment. In Colorado, there
were 11 unique canvassers; in Pennsylvania, there were six. To account for the potential con-
founding effects of canvassers, we estimated the treatment effects using OLS models with
canvasser fixed effects. The results from this alternative specification are presented here. The
results in S1 Table indicate that our findings are robust to accounting for which canvasser
recruited each subject. Whereas our main effect for Pennsylvania was 4.5 points among all
eligible individuals and 8.8 points among those who had never voted, the estimates in S1
Table are 2.4 and 5.1 points, respectively. In Colorado, the treatment effects we present in
the paper are 3.5 points for all eligible subjects and 5 points for those who had never voted,
whereas those effects are 3.4 and 5.3 points in this analysis. Thus, even once accounting for
potential canvasser effects, we still find that turnout is higher among those who received the
pledge treatment.
(TIFF)
Experiments on the effect of pledging to vote on youth turnout
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S2 Table. Robustness of results when removing older individuals from analysis. Recruit-
ment for this experiment happened on college campuses with the aim of mostly mobilizing
young adults. However, recruiters contacted any individual that passed by, not just those who
were younger in age. Accordingly, about 12% of the subjects who were contacted in Pennsylva-
nia and for whom we have age information from the voter file were 30 years of age or older.
In Colorado, about 8% of those contacted and matched to the voter file were 30 or older. S2
Table shows the treatment effects when we remove from the analysis any individuals who are
30 years of age or older. The effects here are for all individuals who were eligible to be treated.
In Pennsylvania, limiting the analysis in this way results in a treatment effect that is somewhat
larger than the 4.5 point effect reported in Table 2 and in Colorado we find a treatment effect
that is identical to the 4.2 point effect that we report in Table 3.
(TIFF)
Acknowledgments
We thank the Environmental Defense Fund’s Defend Our Future Campaign for cooperating
in the administration of this experiment. We also thank Don Green, Greg Huber, Tatishe
Nteta, and Jeremy Pope for providing feedback at various stages of the project.
Author Contributions
Conceptualization: Mia Costa, Brian F. Schaffner, Alicia Prevost.
Data curation: Mia Costa, Brian F. Schaffner.
Formal analysis: Mia Costa, Brian F. Schaffner.
Funding acquisition: Mia Costa, Alicia Prevost.
Investigation: Mia Costa, Brian F. Schaffner.
Methodology: Mia Costa, Brian F. Schaffner.
Project administration: Mia Costa, Brian F. Schaffner, Alicia Prevost.
Supervision: Alicia Prevost.
Visualization: Brian F. Schaffner.
Writing – original draft: Mia Costa.
Writing – review & editing: Mia Costa, Brian F. Schaffner, Alicia Prevost.
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