When Does Increasing Mobilization Effort Increase Turnout? Evidence from a Field Experiment on Reminder Calls

• Author: Gregory A. Huber,Alan S. Gerber,Albert H. Fang,Catlan E. Reardon
• Published date: 01 November 2020
• Date: 01 November 2020
• DOI: http://doi.org/10.1177/1532673X20935786
• Subject Matter: Articles

https://doi.org/10.1177/1532673X20935786

American Politics Research

2020, Vol. 48(6) 763 –778

© The Author(s) 2020

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DOI: 10.1177/1532673X20935786

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Article

Scholars and practitioners working in the domain of cam-

paigns and elections share a growing interest in understand-

ing which Get Out the Vote (GOTV) mobilization tactics are

effective at increasing participation levels and for what rea-

sons. Work on the timing of mobilization efforts (Nickerson,

2007; Panagopoulos, 2011) finds that mobilization closer to

an election is more effective than earlier contact. The inter-

ventions in these studies typically involve a single mobiliza-

tion attempt. In real campaigns, however, citizens may be

inundated by multiple mobilization attempts. This has also

led to growing interest in an important question about the

marginal returns to increasing the intensity of mobilization

efforts: Do additional attempts at contacting voters increase

turnout beyond the effects of a single mobilization attempt,

and if so, why?

Despite increased interest, there are few experimental stud-

ies that address these questions. The limited work that exists

involves phone-based GOTV campaigns and offers mixed

findings. Early research found that a second mobilization

attempt had no effect on turnout relative to an initial attempt

(Green & Gerber, 2001). More recent research has reported

relatively large positive effects of a second round mobilization

attempt on turnout beyond an initial successful call when the

second call provides a reminder to vote (Michelson et al.,

2009). These competing findings, coupled with the relatively

small number of studies on the efficacy of reminder calls,

means there is theoretical and empirical uncertainty.

Existing experimental evidence seems to suggest that a

second round mobilization attempt occurring just prior to an

election is effective at increasing turnout beyond a successful

initial call, but only when the second call is a reminder call

(and perhaps only among those who state they intend to

vote). But the literature is unable to clarify, both theoretically

and empirically, why second GOTV attempts containing a

reminder to vote are effective at increasing turnout beyond

an initial and early GOTV attempt. Nor has it fully tested

whether these effects depend on a citizen’s prior interest in

participating.

Most succinctly, existing experimental designs test bundled

treatments and do not provide leverage to test alternative

causal theories explaining observed effects. Additionally,

scholars have observed the fact that reminder call effects in the

literature are from studies that condition on subjects saying

they intend to vote and have assumed that the effects would

935786APRXXX10.1177/1532673X20935786American Politics ResearchGerber et al.

research-article2020

1Department of Political Science, Institution for Social and Policy Studies,

Yale University, New Haven, CT, USA

2Independent researcher, Yale University, New Haven, CT, USA

3Travers Department of Political Science, University of California,

Berkeley, Berkeley, CA, USA

Corresponding Author:

Alan S. Gerber, Department of Political Science, Institution for Social and

Policy Studies, Yale University, 77 Prospect Street, PO Box 208209, New

Haven, CT 06520-8209, USA.

Email: alan.gerber@yale.edu

When Does Increasing Mobilization Effort

Increase Turnout? Evidence from a Field

Experiment on Reminder Calls

Alan S. Gerber1, Gregory A. Huber1, Albert H. Fang2,

and Catlan E. Reardon3

Abstract

When does increasing mobilization effort increase turnout? Recent experiments find second calls containing a reminder to

vote increase turnout beyond an initial contact. We argue existing studies cannot explain why reminder calls are effective

because they test bundled treatments including a late mobilization attempt, a late mobilization attempt given earlier contact,

and potentially activating reciprocity established in earlier contact. We report results from a two-round voter mobilization

field experiment that allows us to isolate these different mechanisms. We find that reminder calls increase turnout by 1.2%

points among subjects contacted in an earlier attempt, but that enhancing reciprocity by providing a reminder call offer

during an early call does not increase turnout beyond a second call. Additionally, we fail to find heterogeneous effects of

reminder calls by stated preference for a reminder or by stated vote intention, suggesting certain mechanisms do not explain

the effects of reminder calls.

Keywords

voter mobilization, reminder calls, reciprocity, field experiment

764 American Politics Research 48(6)

not exist in the absence of such conditioning, leading them to

emphasize theories about the role of baseline preferences

toward voting. However, these mechanisms are not tested in

existing studies; doing so would require directly and formally

testing whether there are heterogeneous second round

reminder call effects by subjects’ prior stated vote intentions.

In this article, we address these concerns and make sev-

eral important incremental contributions to the literature. We

design and analyze data from a phone-based GOTV experi-

ment conducted by a non-profit, non-partisan organization in

Colorado during the 2014 midterm election. In the experi-

ment, the number and timing of GOTV call attempts (an

early or late GOTV call) and the contents of the initial call

(specifically, whether a reminder call to vote is offered in a

first round call) are randomly manipulated. This experimen-

tal design provides leverage to isolate the causal effects of

varying the level of campaign effort as a function of the num-

ber of calls, varying the timing of calls, and varying the

degree to which an expectation of reciprocity is established

and primed by manipulating the behavioral interactions

occurring between the citizen and the campaign caller. Our

design also provides leverage to test whether attempting a

second round reminder call has heterogeneous effects by

subjects’ stated vote intention.

We report three main empirical findings. First, we find

that attempting a late GOTV call increases turnout by

approximately 1.2% points among subjects successfully

reached in an early GOTV call. This effect is smaller than

some estimates previously reported in the literature, but pro-

vides additional experimental evidence supporting the argu-

ment that second round GOTV calls are effective at increasing

turnout levels conditional on a successful initial contact (in

support of Michelson et al. (2009), but contra Green and

Gerber (2001)). Second, we do not find support for the reci-

procity mechanism. The effect of a second round call is just

as large when a reminder call is offered in an early call as it

is when an offer is not provided in an early call. Third, we

find that the effect of a late GOTV reminder call does not

vary by subjects’ stated vote intention. Thus, the result we

observe in this study leads us to downgrade our belief that

observed second round reminder call effects on turnout are

attributable to either reciprocity or a class of explanations

emphasizing the causative role of intrinsic motivations to

vote or statements about future vote intentions that are

enhanced by a subsequent reminder call.

Existing Research

Does increasing mobilization effort increase turnout? The

literature suggests that a second GOTV attempt providing a

reminder to vote increases turnout among those successfully

contacted in an earlier GOTV attempt. We briefly describe

three experimental studies relevant to this argument and

identify two important questions about existing research.

First, we show that existing work is unable to clarify why

observed effects exist because existing experiments involve

bundled treatments that could operate through multiple

hypothesized mechanisms. Second, we argue that existing

theoretical explanations are incomplete because they inade-

quately distinguish between theoretical mechanisms related

to GOTV contact generally, repeated GOTV efforts, or repeat

interactions with a specific group. We argue that these theo-

retical ambiguities should inform experimental design.

Reminder GOTV Calls Increase Turnout

Green and Gerber (2001, pp. 21–22) conducted the first field

experiment to assess whether increasing mobilization effort

increases participation by testing the effect of a second

GOTV call relative to a single GOTV call on voter turnout

among a sample of registered voters aged 18 to 30. One of

the factors in their original

22×

factorial design randomly

assigned half of the subjects to be called on Monday, the

night before the election ( n= 674), and the other half to be

called on both Sunday and Monday (n=

673

). This manipu-

lation provides leverage to identify the effect of additionally

calling on Sunday versus only calling on Monday on turnout.

They find no effect of the second call on turnout relative to

one call: the estimated average intent-to-treat (ITT) effect of

attempting two calls is −0.3% points (s.e. = 2.4, not signifi-

cant) relative to a one call group mean turnout rate of 75%

and the Complier Average Causal Effect (CACE) of two

calls is −0.4% points (s.e. = 3.1, not significant; estimated

proportion of Compliers = .845) (Green and Gerber, 2001, p.

37, Table 7). This study is unusual in that both calls are timed

to occur proximate to the election and to each other.

In subsequent research, Michelson et al. (2009) argue

instead that multiple mobilization attempts taking the form

of targeted reminder calls increase turnout, and that this

effect is particularly pronounced among registered voters

who are reached by a phone canvasser and who state to the

canvasser that they intend to vote in the upcoming election.

Of the four studies reported by Michelson et al. (2009), two

are relevant to the substantive quantities of interest we inves-

tigate in this paper. We briefly review the design and findings

of each in turn.

In the first of these studies, Michelson et al. (2009) ana-

lyze data from a field experiment conducted in 2003 where

the Public Interest Research Group (PIRG) targeted regis-

tered voters aged 18 to 24. The study involved 2,817 sub-

jects, all of whom were targeted by PIRG in an initial round

of mobilization attempts using both phone and door-to-door

canvassers prior to Election Day. About half of subjects were

randomly assigned to a treatment group for whom PIRG

would attempt follow-up GOTV calls containing a reminder

to vote on Election Day.1 The remaining subjects were

assigned to a control group that received no follow-up call

from PIRG beyond the initial GOTV attempt. Michelson

et al. (2009) report that attempting a follow-up GOTV call on

Election Day increases turnout by 3.8% points ( p< .01 )