Voter ID Laws and Voter Turnout1

Kyle A. Dropp2

1Please do not cite without the author’s permission.I would like to thank Jonathan Rodden, Justin Grimmer, Paul Sniderman, Clayton Nall, Jowei Chen, BobbyGulotty, Arjun Wilkins, Gary Cox and members of the Stanford Methods Workshop for helpful comments.

2Ph.D. candidate, Department of Political Science, Stanford University, dropp@stanford.edu

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Do Voter Identification statutes reduce voter turnout? I demonstrate that the decade-longexpansion of Voter ID statutes has demobilized Democratic-leaning individuals includingyoung adults, renters, the poor and African Americans using individual voting records overa series of four elections (2004-2010). I use a difference-in-differences approach to comparechanges in turnout between 2004 and 2008 among voter subgroups in Voter ID stateswith broader statewide turnout and turnout in states with no election law policy change.This research both clarifies mixed findings in the scholarly literature and introduces a newapproach for documenting how election law changes impact subgroups.

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Thirty-one states have enacted and adopted Voter Identification statutes,3 and strict poli-cies requiring a government-issued ID at the polls have become commonplace. Lawmak-ers in 34 states introduced legislation on the subject and eight adopted new policies in2011 alone, driven by a U.S. Supreme Court decision upholding an Indiana statute4 andwidespread Republican gains in 2010 in state houses.5 The Progressive Era reforms of theearly 20th Century and the reapportionment revolution started by Baker v. Carr (1962)transformed the representative-constituent linkage, and the burst of legislative attentionon Voter ID may fundamentally alter the composition of the electorate. Overall, has theexpansion of Voter ID statutes reduced voter turnout? And, if so, which groups have beendisparately impacted?

Previous research has yielded puzzling contradictory findings because it assesses earlier,more lenient statutes, aggregate county or state-level studies are not able to detect effectsacross voter subgroups and survey-based studies contain measurement and sampling error.6

My research examines both lenient and strict policies over the past decade, minimizessampling error and addresses (and dismisses) many potential threats to validity.

In my research, I aggregate tens of millions of individual level voting records over a seriesof four elections (2004-2010) using a national voter database. I isolate groups with lowID ownership rates such as the working class, renters, African Americans, young adultsand Hispanics using demographic information contained in the voter files. Then, I use adifference-in-differences approach to compare the turnout of these voter subgroups beforeand after a Voter ID law change with turnout statewide and with turnout patterns amongvoter subgroups in states with no policy change.

This paper has two principal findings. First, Voter ID statutes exert a modest but po-litically meaningful demobilizing effect, especially among the poor, young adults, rentersand African Americans. States must demonstrate that ID requirements do not pose anundue burden on voters - the results here indicate that Voter ID laws have modest effectsthat are substantial enough to influence election outcomes in close races. For example, aone percent reduction among African Americans in Ohio, who cast 95%+ of their ballotsfor Democrats, corresponds with a loss of more than 5,000 votes for Democrats in a pres-idential election. My research is the first to demonstrate that Voter ID laws impact theparticipation of a broad swath of the electorate including renters and the poor. The resultsare robust to a wide range of data robustness checks.7

3National Conference of State Legislatures http://www.ncsl.org/documents/legismgt/elect/

Canvass_Apr_2012_No_29.pdf4Crawford v. Marion County Election Board, 553 U.S. 181 (2008)5National Conference of State Legislatures http://www.ncsl.org/legislatures-elections/

elections/voter-id.aspx6For a catalog of studies, see this link http://www.brennancenter.org/content/resource/research_

on_voter_id/7Separate sections address estimation issues related to the non-random assignment of Voter ID policies to

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Second, Voter ID laws are more likely to reduce turnout in midterm elections. This find-ing suggests that widespread mobilization and voter outreach efforts during presidentialcontests can reduce the impact of election laws that impose costs on voters.

This study proceeds as follows. First, I describe the widespread adoption of Voter Iden-tification statutes in the past decade and assess the scholarly literature. Then, I discusshypotheses, research design, data sources and findings. I briefly conclude. Separate sectionsaddress data robustness and potential threats to validity.

Voter ID adoption: 2002 to present

In 2001, only one in four states required that voters provide an ID at the polls.8 andnone of these states turned away voters without a suitable ID. Today, voters in 31 statesmust show a form of identification at the polls, and there has been a decisive trend towardstrict policies asking voters to present a government-issued photo identification.9 Pendingcourt challenges in Mississippi and Wisconsin, 33 states may have Voter ID stautes for theNovember 2012 election. In a close election, these ballot security measures may influenceelection outcomes.

The widespread adoption of stringent Voter ID statutes has been fueled by four factors:the passage of the Help America Vote Act (HAVA) in 2002, a concerted, coordinatedeffort among Republican state legislators and governors to enhance ballot security, nearunanimous public support for ballot security measures and the perception of pervasivevoter fraud among Americans.

The Help America Vote Act (HAVA) of 2002 established minimum federal standards forfirst-time voters, established the Election Assistance Commission (EAC) and replaced out-dated voting systems such as punch cards.10 The act passed with overwhelming bipartisanmajorities in both the U.S. Senate and U.S. House and was signed into law by PresidentGeorge W. Bush in October 2002. The act provided voters with a range of options to reg-ister and verify their identify.11 Citizens who cannot provide an ID or the last four digits

states. I also assess the implications of potential violations of the Stable Unit Treatment Value Assumption(SUTVA) such as the possibility that the assignment status of some units affects the potential outcomes ofother units, and the variation in treatments across groups caused by heterogeneous Voter ID policies.

8National Conference of State Legislatures http://www.ncsl.org/documents/legismgt/elect/

Canvass_Apr_2012_No_29.pdf9National Conference for State Legislatures http://www.ncsl.org/legislatures-elections/

elections/voter-id.aspx10Pub.L. 107-252 http://www.gpo.gov/fdsys/pkg/PLAW-107publ252/html/PLAW-107publ252.htm11First-time voters must provide either a Photo ID, Non-Photo ID, their current and valid driver’s license

number, a state identification number or the last four digits of their Social Security Number.(Help Amer-ica Vote Act, Section 303b http://www.fec.gov/hava/law_ext.txt). Individuals who cannot meet theserequirements will be assigned a unique voter registration number.

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of their Social Security number are assigned a unique voter registration number.

Americans are very concerned about ballot integrity and voter fraud, and Voter ID lawsenjoy widespread public support. Seventy-eight percent of Americans said voters shouldbe required to show an official photo identification on Election Day, including 86 percentof Republicans and 71 percent of Democrats, according to a 2006 Pew poll.12 And fully48 percent of Americans said that voter fraud – people voting who are not eligible orvoters casting multiple ballots – is a major problem, according to a 2012 Washington Postpoll.13

Figure 1 on Page 6 displays changes in Voter ID statutes from 2002 to the present. Statesin white have adopted the HAVA minimum requirement, light blue states require a Non-Photo ID such as a bank statement and blue states require a Photo ID such as a driver’slicense. Dark blue states, the most stringent, require voters to present a Photo ID butprovide few alternatives for casting a provisional ballot.14

Policies vary dramatically across states. In Indiana, a dark blue state, voters must presentan ID issued by Indiana or the United States containing the individuals’ name and photo,along with an expiration date.15 In Washington, a Non-Photo ID state voters may presenta valid Photo ID, voter identification card, utility bill, bank statement, paycheck or gov-ernment document. Further, individuals who cannot provide identification can cast aprovisional ballot.16

12Survey by Pew Research Center for the People and the Press, October 17-22, 2006 based on 2,006telephone interviews.

13The poll was conducted July 18-29, 2012, and based on 2,047 telephone interviews. Thirty-three percentsay it is a minor problem and 14 percent say it is not a problem.

14Alvarez et al. (2007) use an 8-point coding scheme rather than a 4-point classification. They assignstates to the following Voter ID requirements: state name, signature, matching signature, request ID, requireNon-Photo ID, require ID plus signature, request Photo ID, require Photo ID. The four point classificationis more appropriate for illustrating the decade-long trend toward more stringent Voter ID policies.

15If a voter cannot produce this proof of identification, he must return to the election board with proofof identification, or state that he cannot obtain an ID because he is indigent or has a religious objection tobeing photographed. http://www.ncsl.org/legislatures-elections/elections/voter-id.aspx

16http://www.ncsl.org/legislatures-elections/elections/voter-id.aspx

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Figure 1: Voter ID statutes from 2002 to present. White states have no Voter ID statute,light blue states require a Non-Photo ID, blue states require a Photo ID and dark bluestate have Strict Photo ID policies with limited provisional ballot options.

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Figure 1 on Page 6 exhibits three trends: Voter ID policies have spread from the Southto much of the country in the past decade, they have become increasingly stringent inrecent years and their adoption is driven by partisan factors rather than simple diffusionto neighboring states.

In 2002, conservative Southern states including Georgia and Texas were among the onlystates to have Voter ID laws stricter than the Help America Vote Act minimum require-ments. Since then, Voter ID statutes have spread to the Mountain States,the Southwest,and parts of the Midwest. The West Coast and the Northeast are the only regions largelyunaffected by the nationwide drive to strengthen Voter ID laws. In 2011, only three stateswithout Voter ID statutes in place – Oregon, Vermont and Wyoming, did not considerlegislation to strengthen their Voter ID policy.17

Second, Voter ID statutes has become increasingly stringent in recent years. Many earlyVoter ID statutes required only a Non-Photo ID and provided ample opportunities forvoters to cast a provisional ballot. Eleven states now require voters to present a Photo ID,compared with four in 2004 and none in 2002.

Third, there is a strong relationship between GOP control of state legislatures and a state’sVoter ID policy. Twenty-one of the 26 states where Republicans currently control bothlegislative chambers have enacted Voter ID statutes above the HAVA minimum, and all11 states with the most stringent Photo ID or Strict Photo ID requirements have unifiedRepublican legislative control. On the other hand, only 4 out of 15 states with currentunified Democratic control of state houses have enacted Voter ID statutes.18

Biggers and Hanmer (2011) examine Voter Identification statutes from 1972-2011 and findthat partisan factors are more important than diffusion to neighboring states in predictingthe passage of Voter ID statutes: “the switch to a Republican governor has a large positiveeffect on this decision to require identification at the polls” (Biggers and Hanmer, 2011, p.27). Related, Voter ID policies are supported or opposed along party lines. For example,more than 95% of Republican legislators supported Voter ID laws introduced between 2005and 2007, compared with just 2% of Democrats.19 20

17http://www.ncsl.org/legislatures-elections/elections/voter-id-2011-legislation.aspx18I obtained data on the party composition of state legislatures from 2000-2011 from the National Confer-

ence of State Legislatures and merged it with the four-point classification of Voter ID statutes (1 = HAVAminimum, 2 = Non-Photo ID, 3 = Photo ID, 4 = Strict Photo ID). Overall, the correlation between unifiedGOP control of state legislatures in 2011 and current Voter ID policy is .57.

19Brief of Amici Curiae of Historians and Other Scholars in Support of Petitioners. Crawford et al. v.Marion County Election Board et al. Nos. 07-21, 07-25 (U.S., 2007).

20Similarly, on voter identification provisions, the “average difference between the percent of Republicansand Democrats voting yea on the eleven Senate votes relating to HAVA was ninety-one percentage points”(Lee, 2009)

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Scholarly literature

Policymakers and politicians generally believe that Voter ID statutes will influence elec-tion outcomes. Republicans have suggested that Voter ID statutes may flip states fromDemocratic to Republican: “Voter ID, which is gonna allow Governor Romney to win thestate of Pennsylvania, done,” said Pennsylvania House Majority Leader Mike Turzai afterthe passage of a strict statute.

Democrats have used these ballot laws to motivate their party’s base: “If you want everyAmerican to vote and you think it’s wrong to change voting procedures just to reducethe turnout younger, poorer, minority and disabled voters, you should support BarackObama” former President Bill Clinton said when he nominated President Barack Obamaat the Democratic National Convention in September 2012.

And prominent Democrats have compared this legislation to Jim Crow laws: “We arewitnessing a concerted effort to place new obstacles in front of minorities, low-incomefamilies and young people who seek to exercise their right to vote. A poll tax by anothername would smell as vile,” said U.S. Rep. Steny Hoyer (D-Md.), in November 2011.

Despite these statements, a growing, methodologically diverse research literature on VoterIdentification statutes and voter turnout has yielded puzzling, mixed findings. These mixedfindings have resulted from data limitations and the focus on earlier, more lenient statutes.Some research has found that Voter ID laws have a minimal impact on turnout (An-solabehere, 2009; Lott, 2006; Pastor et al., 2010; Mycoff et al., 2009; Milyo, 2007). Theseauthors find that Voter ID statutes are inconsistently implemented, that most adults havesuitable forms of identification and that individuals without IDs are not likely to vote.

Ansolabehere (2009) examines Current Population Survey (CPS) data and concludes that“[v]oter ID appears to present no real barrier to access” (Ansolabehere, 2009). Poll workersrarely ask for ID, he finds, and individuals almost never say they did not vote because theylacked an ID.

Using largely the same methods and data, other authors have found that Voter ID statutesdecrease turnout among subgroups lacking suitable IDs and that more stringent Voter IDlaws exert a larger demobilizing effect (Vercellotti and Anderson, 2006; Alvarez et al., 2007;Logan et al., 2007; Alvarez et al., 2011).

An overarching theme in the literature, however, is that the available data is not powerfulenough to answer this question with confidence.21 Aggregate level studies using counties or

21There are a series of separate reasons why election administration policies may only impact voterson the margins. Few voters actually would be turned away from casting a ballot solely based on 2008state-by-state ID requirements, according to two separate studies. One study estimates that .5% of respon-dents would be prevented from voting (Alvarez et al., 2008) http://www.american.edu/spa/cdem/upload/VoterIDFinalReport1-9-08.pdf while a 2007 study estimates that one tenth of one percent of voters would

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states cannot document the impact of state-level interventions on voter subgroups, whileindividual level survey data includes measurement error from inflated self reports of voterturnout and sampling error caused by small samples.

Erikson and Minnite (2009) call into question the use of cross-sectional data from the Cur-rent Population Survey. They analyze multiple years of CPS data and find no relationshipbetween Voter ID laws and turnout, contrary to previous authors’ conclusions from analysisof the same data: “[W]e see the existing science regarding voter suppression as incompleteand inconclusive. This is not because of any reason to doubt the suppression effect butrather because the data that have been analyzed do not allow a conclusive test” (Eriksonand Minnite, 2009, p. 98).

The expansion of Voter ID statutes is a recent phenomenon, and scholars have not hadmany election cycles to examine their effects: “[S]ince the changes in voter identificationrequirements have really only started since the passage of HAVA in 2002 and the lawwe are most interested in – photo identification requirements – was only implemented in2006, we have only a small amount of information in the available data about how each ofvoter identification requirements might affect participation” (Alvarez et al., 2011, p. 10).Voter Identification Laws may exert their greatest impact years after implementation, whenyoung adults and first-time voters must obtain an ID to cast their ballot. Previous researchhas been unable to test this. Further, the trend toward stricter laws in recent years meansthere have been even fewer data points to study the stringent election policies most likelyto adversely affect turnout.

Hypotheses

Scholars generally cite three reasons why Voter ID statutes may reduce turnout. First,many Americans do not have suitable or up-to-date forms of identification. Second, somecitizens may decide not to cast a ballot because they are confused by the statutes’ re-

be unable to vote because of an ID requirement (Ansolabehere, 2007).Second, most individuals without proper IDs are unlikely to cast a ballot, regardless of whether they

reside in policy or non-policy states, according to Rick Hasen, an election law expert: “It’s not possible toshow, he says, that many people have actually been deterred from voting by these laws. In part, that’sbecause many of the laws are new, and in part it’s because many of the people who lack an ID card tendnot to be interested in voting in the first place” (Firestone, 2012).

Third, a majority of states with ID policies allow voters to cast a provisional ballot, after signing an affi-davit, for instance, which could eventually be counted. Many of the stringent laws with limited provisionalballot options have been passed only in recent months or are pending.

Fourth, studies of Voter ID statutes do not examine the full effect of requiring an ID versus asking forno ID. The Help America Vote Act established minimum identification standards for first-time voters andabsentee voters, so any change in Voter ID policy is relative to those federal minimum standards.

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quirements or concerned about the fairness of the law’s implementation.22 Third, VoterIdentification laws may reduce voter impersonation, one type of voter fraud, at pollingplaces.23 My research focuses on differential ID ownership rates.

Voter ID statutes inconvenience citizens who lack valid IDs,24 and research indicates thatsubgroups such as young adults, minorities, the working-class, renters and the elderly areboth less likely to own a suitable ID25 and favor the Democratic Party.26 These groupsalso tend to be less familiar with the electoral system.27 Cumulatively, this leads to the

22In a Boston Exit Poll, Cobb et al. (2012) find racial differences in the administration of Voter IDstatutes: “We find strong evidence that Hispanic and black voters were asked for IDs at higher rates thansimilarly situated white voters” (?, p. 3). Similarly, Ansolabehere (2009) finds that minorities are morelikely to report that they were asked to present an ID: “Both the 2006 and 2008 surveys show considerableracial differences. In the 2006 general election, 47% of white voters reported being asked to show photoidentification at the polls, compared with 54% of Hispanics and 55% of African Americans. In the 2008Super Tuesday primary states, 53% of whites were asked to show photo ID, compared with 58% of Hispanicsand a staggering 73% of African Americans” (Ansolabehere, 2009, p. 128).

23According to the National Conference for State Legislatures, “Little evidence exists that fraud by imper-sonation at the polls is a common problem” http://www.ncsl.org/documents/legismgt/elect/Canvass_

Apr_2012_No_29.pdf24A survey of voters found that hundreds of thousands of eligible voters face challenges in obtaining proper

IDs to cast a ballot. According to the Brennan Center for Justice at New York University, nearly 500,000voters “in 10 states with restrictive voter ID laws live in households without vehicles and reside at least 10miles from an ID-issuing office open more than two days a week.”http://www.brennancenter.org/content/resource/study_500000_americans_could_face_significant_challenges_to_obtain_photo_id/

25Racial differences: Twenty-five percent of African Americans and 18 percent of adults 65 years and olderlack the government-issued photo ID necessary to cast a ballot in stringent Voter ID states, compared withone in 10 adults overall, according to the Brennan Center for Justice. http://www.brennancenter.org/

page/-/d/download_file_39242.pdf. Also see http://www.brennancenter.org/page/-/d/download_

file_39242.pdf

Pawasarat (2005) finds that African Americans and Hispanics are less likely to have drivers licenses thanwhites in Wisconsin: “Less than half (47 percent) of Milwaukee County African American adults and 43percent of Hispanic adults have a valid drivers license compared to 85 percent of white adults” (Pawasarat,2005, p. 1). White voters, on the other hand, are more likely to have government-issued IDs (Barreto et al.,2007). Five percent of white registered voters have an up-to-date Driver’s License or State Issued ID Cardcompared with 10 percent of African Americans, 11 percent of Latinos and 14 percent of Asian Americans,according to a 2008 study (Sanchez et al., 2011).

Age, income, rental status differences: Residents who have moved are less likely to own suitable formsof identification: “The population that changes residence frequently is most likely to have a drivers licenseaddress that differs from their current residence. This would include lower-income residents who rent andstudents and young adults living away from home” (Pawasarat, 2005, p. 2). For additional evidence, see(Barreto et al., 2007; Sanchez et al., 2011; Pawasarat, 2005)

26According to the 2008 National U.S. House Exit poll, 93% of African Americans voted for Democrats,along with 68% of Latinos, 63% of Asians, 63% of 18-29 year-olds. Adults 65 and over split about evenly,49% Democrat to 48% Republican. Fifty-nine percent of renters identify as Democrats or leaned Democrats,compared with 41% of home owners, according to a Gallup poll conducted January 5-8, 2012. In the samepoll, 50% of home owners self-identified as Republican or leaned Republicans, compared with 31% of renters.

27When there are changes in election administration policies, Americans with higher levels of civic skills,resources or flexibility in work schedule may adapt more readily than those without such skills: “[The] pres-

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first hypothesis:

H1: Varying ID ownership rates across the electorate suggests that Voter IDlaws will reduce turnout among Democratic-leaning subgroups such as youngadults, renters and minorities.

However, campaigns and interest groups react swiftly to election law changes. Voter IDstatutes may not decrease turnout when campaigns and interest groups devote additionalresources toward voter education and outreach aimed at Americans lacking IDs,28 inter-est groups synchronize their efforts with traditional allies,29 or organized interests shifttheir mission to focus on voter outreach and education campaigns rather than persuasionefforts.30

Organized interests have fixed resources, and grassroots mobilization efforts are more in-tense and comprehensive during presidential elections compared with midterms. Therefore,campaigns will have many more opportunities during presidential election campaigns to ed-ucate citizens about Voter ID requirements and assist them in obtaining valid IDs.

H2: Voter ID statutes are more likely to reduce turnout during midterm electionsthan during presidential elections.

Overall, I argue that Voter ID statutes impose a cost on citizens without suitable forms ofidentification. These laws are likely to shift the composition of the electorate in the GOP’sfavor when mobilization efforts are not intense, such as during midterm contests or whenthese Voter ID laws are stringent.

ence or absence of resources contributes substantially to individual differences in participation. Resourcesare, in turn, not equally distributed; some socioeconomic groups are better endowed than others” (Bradyet al., 1995, p. 274).

28During the 2012 presidential election, the Obama campaign has sent teams to educate Americans inVoter ID states: “Field workers for President Obama’s campaign fanned out across the country over theweekend in an effort to confront a barrage of new voter identification laws that strategists say threatenthe campaign’s hopes for registering new voters ahead of the November election” (Shear, 2012). Moreover,the AFL-CIO “vowed to mount their biggest voter registration and protection efforts ever to counter these[Voter ID] laws” (Greenhouse, 2012).

29Election law changes increase interest groups’ coordination efforts with traditional ideological al-lies: “The federation’s [AFL-CIO] leaders said they would work closely with other groups, including theN.A.A.C.P. and the National Council of La Raza, to maximize voter turnout and provide whatever help isneeded to enable elderly, disabled and poor Americans to get voter IDs” (Greenhouse, 2012).

30During the 2008 presidential campaign, The National Association for the Advancement of ColoredPeople (NAACP) chose to “focus on voter education and outreach ahead of this year’s presidential electionin the wake of a U.S. Supreme Court ruling on voter identification laws,” according to a statement (Haines,2008).

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Research Design

In this section, I outline the difference-in-differences identification strategy (Ashenfelterand Card, 1985)31 and describe the assumptions I am making to estimate treatment ef-fects.

Suppose State S implements a Voter Identification law a few months after the 2004 presi-dential election. We want to understand whether the statute reduces turnout among collegestudents, a group that disproportionately lacks valid forms of identification. Our outcomevariable is the percent of eligible adults who cast a ballot, the treatment group is collegestudents in State S and the control group is all other residents in State S. This difference-in-differences approach tests whether the policy intervention in State S decreases collegestudents’ turnout relative to statewide turnout. If turnout in State S was 50% for bothcollege students and statewide in Nov. 2004, 50% statewide in Nov. 2008 and 45% forcollege students in 2008, as displayed in Figure 2 on Page 13, we conclude that Voter IDpolicies reduced turnout by 5% among college students.

This design’s main shortcoming is that factors unrelated to State S ’s new policy mayaffect the political participation of college students relative to statewide turnout. TheObama campaign’s mobilization efforts in 2008, for example, buoyed turnout among collegestudents nationwide. Therefore, a model focusing solely on policy states could produce thespurious result that Voter ID laws boost turnout among college students.

We improve the first approach by using an additional control: one or more non-policyStates ∼S, as shown in Figure 3 on Page 13. Then, we can examine whether the change incollege student turnout relative to statewide patterns is larger in policy states S than innon-policy states ∼S. This accounts both for factors unrelated to the Voter ID policy thataffect turnout among the subgroup nationally, such as Obama mobilization efforts, andfeatures unique to State(s) ∼S that either increase or decrease turnout statewide, such asa competitive gubernatorial race or a weak economic climate.

In this hypothetical, turnout among college students rises across policy and non-policystates; however, it rises much more sharply in non-policy states. We conclude that VoterID laws decrease the turnout of college students. The difference-in-difference-in-differencesestimates (DDD) has four components

δ = [(∆yS,G − ∆yS,∼G] − [(∆y∼S,G − ∆y∼S,∼G]

where δ is the estimator, ∆y is change in mean turnout before and after an intervention,State(s) are either S (policy) or ∼S (non-policy) and Group(s) are either G (subgroups

31Difference-in-differences is used widely in economics and scholars have studied Voter ID policy imple-mentations with this research design.

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Figure 2: Voter turnout in policy statesamong students (blue) and statewide(red)

Figure 3: Voter turnout in policy states(right) and non-policy states (left) amongstudents (blue) and statewide (red)

such as college students) or ∼ G (statewide).32

The first quantity is the change in turnout for a voter subgroup (i.e., college students) inPolicy State(s) S before and after the intervention, while the second sum is the change inturnout statewide in Policy State(s) over the same period. The third quantity is changein the voter subgroup’s turnout in non-policy State(s) ∼ S during the same time frame,whereas the final sum is the statewide change.

We find the population analog by taking the expected value of the four quantities. Thisbasic approach can be extended to study different elections, alternate voter subgroups orother state-level election law interventions. Finally, we can also estimate the treatmenteffect via OLS using a series of indicator variables and interactions shown below

y = β0 + β1S + β2G+ β3S ∗G+ λ0T + λ1T ∗ S + λ2T ∗G+ λ3T ∗ S ∗G+ u (1)

where S (State) is either a policy or non-policy state, G (Group) is either statewideturnout or turnout among the disadvantaged group, T (Time) is pre-intervention or post-intervention and λ3 is the coefficient of interest from the triple interaction of State, Group

32I separately estimate ∆y for turnout changes between Nov. 2004 and Nov. 2008, between Nov. 2006and Nov. 2010 and between Nov. 2004 and Nov. 2010.

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and Time. A negative coefficient on λ3 indicates that state Voter Identification laws de-crease turnout among a particular subgroup.

In summary, I use a difference-in-differences estimator to compare the change in voterturnout before and after a policy change among specific subgroups such as African Ameri-cans with statewide voting trends. Furthermore, I analyze individual level voting patternsboth in states implementing a new Voter ID policy and in states where election law re-mained constant over the same period.

Potential threats to validity

In a controlled, randomized experiment, the experimenter randomly assigns individuals toconditions and exercises control over the treatment, while subjects are not aware of theirtreatment assignment. Unfortunately, many questions under inquiry in political sciencecannot meet the exacting standards of a controlled, randomized experiment. In this section,I address and reject a series of potential threats to validity caused by the observationalnature of this study.

First, since the individual level observations are grouped within the states in which theVoter ID implementation occurs, we cannot assume that errors are independently andidentically distributed. Estimates obtained without clustering observations result in down-ward biased standard errors because individual observations in clustered data contributeless information to a model than data without clustering.33 Erikson and Minnite (2009),for example, find that Voter ID studies using robust rather than clustered standard errorsunderstate the size of standard errors by a factor of seven, influencing whether findingsare significant or not (Erikson and Minnite, 2009, p. 92). Overall, when using state orcounty-level aggregate data or responses from the Current Population Survey (CPS), thecomputation of standard errors can determine whether findings are statistically meaningfulor not.

I use national voter file data, and the standard errors based on a proportion of tens ofmillions of observations are miniscule. For example, we could multiply the standard errorof a proportion of 10 million individuals by a factor of 30 and still obtain a statisticallysignificant finding for a one percentage point treatment effect. The main models in thisstudy estimate standard errors utilizing a cluster bootstrap at the state and county, whichcauses a modest increase in the size of the standard errors.34

33Research in social science has shown that not accounting for clustering can bias standard errors (e.g.,Carsey and Wright, 1998; Green and Vavreck, 2008)

34I compute standard errors by using a series of different clusters. First, I aggregate individual level datato the county level. Then I resample observations using a bootstrap at the state and county level. Second,I aggregate individual level data to the ZIP Code level. Then, I resample observations using a bootstrap atthe state and ZIP Code level. The bootstrap resamples entire clusters of observations rather than individual

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Second, in an experiment, there is random assignment and treatment and control groupsshould be similar across covariates. Since Voter ID laws are more likely to be adopted inconservative states, it is possible that elites are targeting states with voter subgroups likelyto be affected by the policies or with historically low levels of voter turnout.35 The evidencesuggests that Voter ID laws have been driven mainly by the partisan composition of thestate legislature rather than specific characteristics of the state’s electorate. Further, thedifference-in-difference approach accounts for variation in turnout rates across states andvoter subgroups. Previous studies of Voter ID statutes have used difference-in-differencesestimators to address problems associated with non-random assignment (Alvarez et al.,2011).3637

Third, the stable unit treatment value assumption (SUTVA) holds that the assignmentstatus of any unit does not affect the potential outcomes of other units. The clusteringof policies at the state level, the broad awareness of Voter ID statutes nationwide,38 andthe widespread adoption of these election laws in the past decade calls into question thevalidity of this assumption.39 It is likely, for instance, that learning of a Voter ID policyin a neighboring state could confuse voters and deter them from voting, even if they livein a state with no Voter ID policy. This actually would bias our estimate in the oppositedirection and make it more difficult to conclude that Voter ID statutes decrease turnoutamong voter subgroups.40 Second, as I discuss in the next section, I study the impact of

observations and modestly increases the size of the standard errors.35For instance, Voter ID laws may negatively impact turnout among African Americans in Georgia more

than African Americans in North Carolina. If legislators pass a law in Georgia but not in North Carolina,then the estimated treatment effect will be biased upward.

36Alvarez et al. (2011), for example, use a difference-in-differences estimator with Current PopulationSurvey data to estimate the impact of Voter ID statutes: “Finally, identification requirements are notrandomly assigned across states. This is a problem if states with historically lower turnout also tend toadopt stricter identification requirements, then we will have trouble isolating whether the low level of turnoutis due to the identification requirement or to other factors that lead a given state to have lower turnoutrates. The estimation strategy used exploits the temporal and geographic variability in voter identificationrequirements to sidestep the problem on non-random assignment. This is referred to as a difference-in-differences estimator and our analysis is built on a generalization of this procedure. In particular, we use amultilevel model – also referred to as a random effects model – to assess how voter identification requirementsaffect participation by registered voters, using data from four years of recent CPS Voter Supplement data(Alvarez et al., 2011, p. 10).

37We also can address this issue by matching on covariates with Catalist’s 1% sample, which containsdetailed information on more than two million voters. With this approach, the sole difference between unitsis the assignment to treatment.

38Twenty-one percent of Americans said they heard or read a lot about states putting in place new photoidentification requirements for voters, according to a Washington Post poll in 2012. The pool was conductedJuly 18-29, 2012 and based on 2,047 telephone interviews. Twenty-seven percent said they heard or readsome, 15% said not much and 36% said they had heard or read nothing at all.

39“The [potential outcome] observation on one unit should be unaffected by the particular assignment oftreatments to the other units” (Cox 1958). If assignment status influences potential outcomes, then thereare several compound treatments, each of which involves a different assignment.

40It is possible, however, that reports that African Americans are assigned to a Voter ID treatment may

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relative changes in the stringency of Voter ID statutes, not the absolute level of the policy.It is unlikely that voters residing in Non-Photo ID states who hear of a Photo ID policyimplementation in a neighboring state will change their voting behavior.41

The next section discusses the elections and constituencies examined in this study.

Data

Assembling a Voter ID Database

I assemble a database of Voter ID policies from 2002 to the present using sources such as theNational Conference of State Legislatures, LexisNexis and the work of previous scholars.The time series policy database facilitates statistical tests examining the impact of changesin Voter ID policy on voter turnout.42

The National Conference of State Legislatures places ID requirements in four categories:No Voter ID law, Non-photo ID law, Photo ID law and Strict Photo ID law. I follow theirmethodology.43 Overall, 13 states changed their Voter ID statutes between the 2002 and

mobilize African Americans in Mississippi, a non-policy state, leading to a biased estimate of the treatmenteffect

41Finally, the second part of SUTVA holds that there is no variation in treatment across groups, thatthe treatments for all units are comparable. SUTVA posits a fixed potential outcomes for units assigned toeither treatment or control. Variation in treatment effects means that there are actually multiple, separatetreatments. Voter ID statutes are multi-faceted and diverse, and each state has unique minimum andmaximum requirements, making it nearly impossible to calculate a single average treatment effect. Theseconcerns are highlighted by Alvarez et al. (2011). Alvarez et al. (2011) address the variation in treatments:“[T]here are many methodological problems unique to this data, one of which is the ordinality of voteridentification requirements. As is apparent from the listing of the types of regimes, it is not the case that astate either requires identification to vote, or does not. States require many different levels of identificationfrom simply stating one’s name to showing a picture identification. This further complicates the question,as we must determine not just one effect but several potentially incremental effects. Second, states maydiffer in their implementation of similar requirements. While one state may consider a student identificationcard or discount club membership card to be valid photo identification, another state may only recognizegovernment-issued photo identification cards” (Alvarez et al., 2011, p. 9-10)

42Assembling a database of Voter ID statutes for each midterm and presidential election since 2002 is notan easy task. States have unique minimum requirements, maximum requirements and policies for handlingprovisional ballots, multiple courts may render judgment on newly enacted Voter ID policies, and electionofficials such as the Secretary of State can modify policies in the days leading up to an election. In a reportto the Election Assistance Commission, the authors note the complexity of Voter ID policy: “We recognizethe difficulties in summarizing each state’s voter ID requirements. The problem is illustrated by the numberof footnotes to Table 1 below. The variety of statutory and regulatory details among the states is complex”(Eagleton Institute report to the EAC, p. 20).

43National Conference on State Legislatures. http://www.ncsl.org/legislatures-elections/

elections/voter-id.aspx The strict photo option refers to states that do not allow voters to cast provi-sional ballots unless they present a photo ID.

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2004 election, seven strengthened their laws between 2004 and 2006, two tightened theirpolicies between 2006 and 2008 and three implemented additional Voter ID provisionsbetween November 2008 and November 2010.44 A few states eased their policies duringthe period.

I examine the impact of relative changes in Voter ID policy from one of the four categoriesto another.45 Other scholars have examined the impact of eight different types of Voter IDlaws (Alvarez et al., 2011), and my coding approach can be extended to measure both theimpact of a change in a relative and absolute sense.46

Voter File and Census Data

My primary elections data source is Catalist, a national voter database containing observa-tions for 180+ million registered voters.47 The query-able database includes detailed voterhistories, along with demographic and commercial data appended to each name.48 Overall,the official tallies and demographic variables reported in the Catalist database are highlyaccurate.49

442002-04: AZ, MT, SD, ND, HI, CO, AR, LA, AL, FL, TN, SC, MD; 2004-06: WA, AZ, NM, FL, IN,OH, HI; 2006-08: MI, GA; 2008-10: ID, OK, UT.

45The majority of states in the sample changed their Voter ID statute by one increment in the four-pointclassification scheme. Separate models demonstrate that the impact of changing one increment is similarto changing multiple increments.

46Alvarez et al. (2011) have developed an eight point classification scale based on the strictness of thestatute and have categorized each state from 2000 through 2006. Their scheme includes the followingcategories, ranging from the least intrusive to the most stringent: 1) voter states name, 2) voter signs name,3) voter signs and signature match, 4) voter is requested to present proof of identification or registrationcard, 5) voter must present proof of ID or voter registration card, 6) voter must present proof of identificationand signature match, 7) voter is requested to present photo id, and 8) voter is required to present photo id(Alvarez et al., 2011).

47I received access to Catalist through Stanford University’s Academic Subscription.48Ansolabehere and Hersh (2010) describe Catalist’s basic data collection process and the rigorous proce-

dures they implement to validate the data: “Several times a year, Catalist purchases the publicly availablevoter registration files made available by each state or county election office...Catalist then cross-referencesthe registration lists with other public records, such as the National Change of Address (NCOA) databasemaintained by the Post Office and the Social Security death index. Movers and deceased voters are flagged.Catalist matches the registration files to commercial records from data aggregation firms that compile listsfrom retailers and direct marketing companies. This allows the firm to correct the records of individualswho may have a typo in their registration record or may have registered with a nickname rather than theirlegal name” (Ansolabehere and Hersh 2010, p. 5)

49There may be a slight discrepancy between the official vote tally and the number of votes cast in thedatabase due to voter purges: “A vote tally from a registration file excludes the votes cast by citizens whowere purged from the file since the election. For instance, a person who voted in 2006 but was since removedfrom the rolls would not be included in the county on the registration list but would have an official ballotcounted. This presents a minor problem since it only applies to voters who confirmed with the registrarthat they moved” (Ansolabehere and Hersh, 2010, p. 15).

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Previous research on the impact of statewide policy interventions has utilized county orstate level data. These data are not well suited for detecting heterogeneous treatment effectsand are susceptible to ecological inference concerns. These Catalist aggregations provideprecise, accurate outputs of voter turnout with significantly lower sampling error thanstate-level estimates from the Current Population Survey’s November supplement.

I assembled a database from 2004 through 2010 and extracted data across the followingbackground variables: race/ethnicity, age, family income, owner / renter, length of resi-dence and more.50

Catalist Voter Groups.I isolated the number of voters in the following racial groups: African American, Hispanic,White and Nonwhite.51 The racial data in the Catalist database is derived from twosources: self-identified responses in voter files and CPM Ethnics race prediction software.The race variable in the database uses self-identified race in many Southern states, whereresidents list their racial status when registering to vote. In other states, however, CPMEthnics assigns a race based on a highly accurate algorithm including the respondent’sfirst name, middle name, last name, age and characteristics of their Census geography.52

We will have the highest level of confidence when using racial breakdowns based on datacoming from the South, where voters self-report their ethnicity. Hersh (2011), for example,finds that the race variable included in the Catalist data file is accurate between 91% and96% of the time in Southern states.53

States vary in the discrepancy between vote tallies and official results, though the discrepancy is lessthan 5% in most states: “The 2008 and 2006 vote history discrepancy rates vary considerably by states. InOregon, North Carolina, Rhode Island, Delaware, and many other states, discrepancies are at a minimum,representing fewer than 5% of all votes. However, in other states like Mississippi, New York, and Texas,the 2008 discrepancy rate is closer to 10%” (Ansolabehere and Hersh, 2010, p. 15). The worst performersare Colorado, Maine, Mississippi and North Dakota.

50I collected election returns for the 2004 presidential election, the 2006 midterm election, the 2008presidential election and the 2010 midterm election. Therefore, I can compare the relative impact of Voter IDstatutes may exert during presidential contests, midterm elections and multiple cycles after implementation.

51Separate models account for shifts in statewide population size by using annual Census data from theAmerican Community Survey listing total Voting Age Population and Voting Eligible Population by racialgroup as a denominator.

52Given the geographic concentrations of Americans by race, the resulting predictions are highly accurate,though, not without error. Here is a research notes from CPM Ethnics: “In external blind testing againstself-reported ethnicity identification, CPM Technologies solutions have shown over 20% more coverage thanother established ethnicity appending services...CPM Ethnics software can find over 75% of the AfricanAmericans in lists and still maintains an accuracy of over 80%. CPM’s algorithms are based upon modernmachine learning techniques and are built using tens of millions of samples with known race.”http://cpm-technologies.com/cpmEthnics.html

53“The exact model Catalist uses to predict race is proprietary, but we can check the quality of theprediction using survey responses that have been matched into the Catalist database. The 2009 CooperativeCongressional Election Study (CCES) was matched into Catalist’s database. For the registrants with listedraces, 96% of voters’ self-reported races were the same as the publicly listed races. For the registrants whoseraces were predicted with confidence, 91% had the same self-reported race as predicted by Catalist’s model.

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I used birth dates listed in voter files to separate voters into the following age cohorts:adults under 25, 25-34, 35-44, 45-54, 55-64, 65-74, 75-84 and 85+.54 I accounted for shiftsin statewide population size by age cohort by using annual Census data from the AmericanCommunity Survey.55

Adults who move more often are more likely to have IDs with outdated addresses. I usedhousehold level commercial data to isolate adults who had lived in their current householdfor the following periods of time: less than one year, one to five years, six to 10 years, 11 to20 years and more than 20 years. Similarly, I identified individuals who were either rentingor who owned their residence.

Scholars have hypothesized that Voter ID statutes will place an undue burden on workingclass and poor Americans. I isolated household incomes in the following ranges usinghousehold level commercial data: less than $5,000, $5,001 to $12,50, $12,501 to $20,000,$20,001 to $30,000, $30,001 to $40,000, $40,001 to $60,000, $60,001 to $100,000 and over$100,000.56

Population Denominators.I estimate models with four sets of population denominators. Calculating four separatedenominators, each with its own strengths, weaknesses and biases, increases my confidencein the main results. The findings across the four denominators are very similar.

The first approach uses the change in total votes cast in a subgroup in the Catalist databaseover time. This simple, straightforward approach contains limited sampling error becauseit relies on Catalist aggregations; however, it does not fully account for changes in statesubgroup populations between November 2004 and November 2010.57

Though the match between self-reports and the Catalist data is not in perfect agreement, it is sufficientlyaccurate that each racial group in the Catalist database can be divided in two...” (Hersh, 2011, p. 9-10).

54Nearly all records contain a birth date. Records with missing age, however, were supplemented usinga model including the number of years the individual has been registered to vote, the age of the head ofhousehold and the individual’s first name. Importantly, I calculate the age of adults separately for eachelection. Future analyses can utilize a cohort analysis tracking turnout of the same group of adults over 65,for instance, over time.

55Ansolabehere and Hersh (2010) find that “1 in 7 records does not have a listed birthdate, and for manyvoters who do have a listed birthdate, the date entered is inaccurate.” (Ansolabehere and Hersh, 2010, p.2). The primary inaccuracy, however, is that the voter’s birthdate was entered as the first of the month oras January 1.

56Both the household income data and the rental status data are largely based on Census block groupcharacteristics. There are more than 200,000 Census block groups, and there is a high level of spatialclustering of income and rental status. Therefore, the data is likely highly accurate and not affected by thefact that the estimates are obtained from data not at the individual level.

57State subgroup populations change over time, largely due to people changing residence. If, for instance,the number of African Americans in Voter ID states decreases at a higher rate than in non-policy states,we may erroneously conclude that Voter ID laws decrease turnout. For this to affect treatment estimates,though, there have to be systematic differences in population changes across Voter ID and non-policy states.

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The second approach divides the total votes cast in each subgroup by annual estimates ofthat group’s Voting Age Population (VAP) and Voting Eligible Population (VEP) from theAmerican Community Survey (ACS). While this approach accounts for changes in subgrouppopulations over time, it introduces sampling and selection biases. For example, the ACS’sestimates have margins of errors that could swamp a modest treatment effect; further,voting age population estimates inflate the denominator by including groups ineligible tovote such as the large proportion of minorities that are incarcerated or college studentswho are living in one state but are registered to vote in another.58

The third approach divides the total votes cast in each subgroup by the number of reg-istered voters in Catalist’s national database. This approach estimates the change in thepercent of registered voters who cast a ballot, accounts for under coverage in ACS estimatesand reduces sampling error. However, across both states and voter subgroups, there maybe differential rates of inactive voters, ineligible voters, dead voters or purged voters onregistration rolls.

The fourth approach divides the total votes cast in a subgroup by the number of individualsin that subgroup in Catalist’s database with a voter history. With this estimation strategy,we reduce the amount of deadwood in voter registration files because we only includecitizens who have voted at least once between 2002 and 2010.59

Results and Figures

This section isolates groups that scholars have hypothesized will be disparately impactedby Voter ID statutes, such as African Americans, young adults, adults over 65, Hispanics,renters and others. I compare the change in turnout of these subgroups before and after thepolicy intervention with broader statewide turnout and with turnout among similar groupsin control states. I examine the impact of Voter ID statutes separately for presidential andmidterm contests. I finally test the long-term impact of legislation by examining changesin turnout among voter subgroups four years after a policy implementation.

Difference of means

Table 1 displays each component of the difference-in-difference-in-differences estimator.60

First, we estimate the change in turnout among a subgroup, African Americans, before and

58Again, these selection biases are only problematic from inference if there are systematic differencesacross Voter ID and non-Voter ID states. Sampling error can be accounted for by repeated simulations.

59As in the third approach, it is still possible that purging or removal of voters occurs at different ratesacross states and voter subgroups.

60Each component is weighted by population.

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after a policy change. Then, we estimate the change in turnout statewide in policy states.The third and fourth components are group and statewide turnout changes, respectively,in states with no policy implementation. The final estimate of -.005, or half a percentagepoint, the “DDD estimator,” is the impact of Voter ID statutes among African Americansbetween 2004 and 2008.

Table 1: Change in mean turnout for African Americans and statewide, 2004-08Policy States Non-policy states2004 2008 ∆y 2004 2008 ∆y

African Americans 0.583 0.675 0.092 0.532 0.629 0.097

Statewide 0.597 0.634 0.037 0.574 0.611 0.037

0.055 0.060

DDD estimator -0.005

Figures

The figures below display treatment effects by subgroup for three separate election compar-isons: presidential (2004-08), midterm (2006-10) and midterm (2004-10). The first gaugesthe impact of Voter ID laws during presidential contests, while the latter two address theimpact of Voter ID during midterm elections. In each figure, I aggregate turnout amongtens of millions of records in the national voter file by the respective subgroup. Given thesize of the data, the confidence intervals are extremely small.

The primary model specifications compare turnout between the November 2004 and Novem-ber 2008 presidential elections. During this period, nine states tightened their ID policiesand one relaxed its policies. Overall, I find that Voter ID policies exerted a limited impacton turnout during these presidential elections.

The second specification compares turnout between the November 2006 and November2010 midterm elections. During this period, five states tightened their ID policies and onerelaxed its policies. These states include Georgia, Idaho, Michigan, Oklahoma and Utah.Mobilization efforts are less intense during midterm campaigns, and I find that Voter IDlaws are more likely to reduce turnout when such mobilization efforts wane.The relativestrictness of laws implemented between 2004 and 2008, and those adopted between 2006and 2010, is similar. Therefore, the differential effects sizes between the two cycles appearto be driven by changes in mobilization rather than increased strictness of election lawpolicies. The third specification, which compares turnout between 2004 and 2010, yieldssimilar results to the second set of models.

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This section proceeds by analyzing the impact of Voter ID statutes across Americans’ age,income, length of residence, race and home ownership.

AgeFigure 4 on Page 23 displays the treatment effects across five age cohorts.61 The x-axisdisplays the percent change in voter turnout for each election and the panels present threeseparate election models.

The treatment effects in the 2004 - 2008 comparison (left panel) are small and suggest thatVoter ID statutes have a limited impact on turnout across age cohorts during presidentialelections. The youngest and oldest age cohorts are slightly more likely to vote, perhapsdue to enhanced mobilization efforts in these Voter ID states.

The midterm comparison (center panel) suggests that Voter ID laws reduce turnout amongyoung adults but may lead to a slight increase in turnout among older adults. This ac-centuates the Republican Party advantage. For example, Voter ID laws reduced turnoutamong adults under 35 by two percentage points between 2006 and 2010, compared witha two percent increase among adults over 65. This suggests that counter-mobilization ef-forts inspired by Voter ID statutes may slightly increase turnout among Republican-leaningolder adults.62 The right panel looks nearly identical to the center panel, with Voter IDstatutes reducing turnout among adults under 35 and adults but generally causing slightincreases among older citizens.

This figure illustrates the advantages of using granular aggregate data. While Voter IDpolicies do not appear to affect overall turnout (mean treatment sizes are around 0), thereare heterogeneous effects across age cohorts.

61Given the low number of voters under 25, I collapsed the under 25 and 25-34 cohorts.62Adults over 65 were the age cohort least likely to support Obama in 2008.

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Figure 4: Voter ID treatment effects by age cohort and election.

Household incomeFigure 5 on Page 24 displays the treatment effects across six household income strataranging from less than $20,000 annually to household income exceeding $100,000. Theeffects in the 2004 to 2008 comparison suggest that Voter ID laws actually increased turnoutamong citizens in the lowest income strata. It is possible that during this cycle campaignstargeted such voters in Voter ID states. Voter ID laws do not appear to influence turnoutbetween 2004 and 2008 across other income strata.

Among states that changed their policy between 2006 and 2010, Voter ID laws dispropor-tionately demobilize poor and working class voters. Americans in households earning lessthan $20,000 annually are about three percentage points less likely to cast a ballot in VoterID states. Voters in the highest income strata exhibit slight turnout increases during thissame period. The demobilizing of working class Democratic voters, combined with themobilization of wealthier Republican voters, heightens the impact of these statutes on thecomposition of the electorate.

The effects are even larger in the model comparing 2004 turnout with 2010 turnout. In

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states that implemented Voter ID statutes between 2004 and 2008, turnout is reducedamong poor voters by approximately five percentage points.

Figure 5: Voter ID treatment effects by income strata and election.

Length of ResidenceFigure 6 on Page 25 displays the impact of Voter ID statutes based on the length of timethe current resident has lived in his or her current household. Individuals who have residedin their current household for many years are more likely to own an ID listing their currentaddress.

Individuals who have lived in their current residence for less than one year are negativelyaffected by Voter ID statutes in all three panels, though the effects are most negative amongadults who have lived in their household for six to 10 years. Overall, however, the plots(especially the center and right panels) suggest that Voter ID statutes depress turnoutamong residents who have lived in their current household for a relatively short amount oftime. Across the three election comparisons, we never witness declines in turnout amongindividuals who have lived in their current residence for more than 10 years.

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Figure 6: Voter ID treatment effects by length of residence and election.

RaceFigure 7 on Page 26 displays the impact of Voter ID statutes for African Americans, His-panics, Whites and all non-whites. The effects are rather small across the three panels.However, the right panel suggests that Voter ID laws cause an approximately 2 percentagepoint decrease among African Americans while not affecting turnout among white Ameri-cans between November 2004 and November 2010. Hispanic voter turnout is not affectedin any of the specifications.

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Figure 7: Voter ID treatment effects by race and election.

Own / rentFinally, I aggregated data based on whether respondents were currently renters or ownersof their households. Figure 8 on Page 27 shows that Voter ID statutes do not affectturnout for either group for the 2004 or 2008 presidential elections; however, in the midtermcomparison and the 2004-10 comparison, there are significant differences between turnoutpatterns among renters and owners. The data suggests that Voter ID policies decreasemidterm turnout among renters by about seven percentage points and decrease turnoutbetween 2004 and 2010 by 10 percentage points, an even larger treatment effect.

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Figure 8: Voter ID treatment effects by home ownership and election.

Census Block Group data

The previous section analyzes individual level Catalist voter file information. I conduct aseparate analysis using aggregate data at the Census block group level. There are more than200,000 block groups across the country, meaning that the average population for theseblock groups is approximately 1,500 persons. This secondary analysis presents evidencebroadly supportive of the findings in the previous section and introduces a few new measuresof interest such as block group level household income.

Block Group election returns

I obtain Block Group elections returns from the Catalist Voter database. Generally, Idivide variables such as income, racial composition and home ownership rates into bins for

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which there are equivalent U.S. Census Bureau measures. Then, I take the sum of the totalvotes across the four general election cycles.

I download Census block group data using the 2006-2010 American Community Survey’sfive-year block group estimates and sum the number of individuals living in block groupswith certain characteristics.63

We expect that areas concentration with African Americans, lower income individuals andrenters will experience turnout declines subsequent to Voter ID statute implementations.On the other hand, block groups populated with white Americans, the wealthy or homeowners should experience little to no impact in their political participation rates.

Table 2 on Page 29 displays the change in turnout based on analyses at the block grouplevel.64 The top panel of Table 2 displays voting patterns for individuals based on thehousehold income in their block group. We expect that areas with lower incomes willexperience a decline in turnout relative to areas with wealthier residents.

Between 2004 and 2008, turnout in block groups in Voter ID states with average householdincome under $25,000 annually decreased by 1.5 percentage points. In middle class andupper class block groups, the Voter ID intervention either had a minimal effect or a slightpositive impact. Voter ID policies reduce turnout among the lowest two income categoriesfor the midterm election comparison and the third comparison as well, while voter turnoutamong richer households actually increases in policy states.

The middle panel of Table 2 displays turnout patterns based on the proportion of AfricanAmericans residing in a decile. We expect that areas with mainly African Americans willexperience a decline in turnout relative to areas that are homogeneously white. Overall,the data confirm this pattern, though the substantive effects sizes are quite small. Between2004 and 2008, for example, turnout was unaffected among Americans living in blockgroups with fewer than 10% African Americans. On the other hand, turnout declined 1.1%in block groups containing 40-50% African Americans and by .5% in block groups with atleast half African American residents. The results for the midterm election largely confirmthis pattern.

63For example, I measure the proportion of African Americans living in each block group, divide themeasure into deciles and aggregate the total number of individuals living in each decile. These estimationsprovide a denominator for the Catalist block group election returns discussed in the previous subsection.

64As a rule, I only display block group categories that contain at least five percent of the Americanpopulation. This leads me to pool a few results. For example, four percent of Americans live in blockgroups with fewer than 10% home owners. I sum election returns for all Americans living in block groupswith fewer than 30% homeowners. This procedure does not change any substantive takeaways. Similarly,I sum election returns for all Americans who live in block groups with an average household income above$125,000. The Census measure goes up to $250,000, but very few Americans resides in block groups withmedian household incomes this high. Finally, I sum election returns for Americans living in block groupwith at least 50% African Americans. Seven in 10 Americans live in a Census block group with fewer than10% African Americans, meaning that the remaining nine deciles do not have huge populations.

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Table 2: Block Group Analysis: The percent change in turnout based on Census BlockGroup characteristics

Household Income at the Block Group Level

< 25k 25-50k 50-75k 75-100k 100-125k 125k+2004 vs. 2008 -1.5 0 .5 .5 -.1 -.32006 vs. 2010 -.9 -2.0 -.4 1.4 1.9 2.22004 vs. 2010 -.3 -1.3 .3 .2 .3 3.0% population 7 39 31 14 7 4

% African American at the Block Group Level

0-10 10-20 20-30 30-40 40-50 50-1002004 vs. 2008 0 .1 -.4 -.9 -1.1 -.52006 vs. 2010 .1 .1 -.2 -.5 -.4 -.82004 vs. 2010 .2 -1 -.6 -.4 .3 0% population 70 11 6 3 2 8

% Homeowners at the Block Group Level

0-30 30-40 40-50 50-60 60-70 70-80 80-90 90-1002004 vs. 2008 .2 -.3 -.3 .1 .2 .2 .2 -.32006 vs. 2010 -.1 .2 -.1 -.1 .1 .3 .2 -.52004 vs. 2010 -.7 -.8 -.5 -.9 -.4 .3 -.3 1.3% population 11 5 7 9 11 16 21 20

The bottom panel of Table 2 displays turnout patterns based on the proportion of home-owners at the block group level. We expect that areas populated with renters are morelikely to experience decreases in turnout compared with areas with all homeowners. Theevidence to support this claim is weaker than in the top two panels of the table. In themain presidential and midterm comparison, the proportion of home owners in your blockgroup does not appear to impact turnout; however, in the 2004-10 comparison, residentsresiding in block groups with fewer than 50% homeowners experience an approximately1 percent decline in turnout, while individuals living in block groups with 90%+ homeowners experience a 1.3% increase in turnout.

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Discussion

This research suggests that the decade long strategic effort among Republicans shifted thecomposition of the electorate in the GOP’s favor. I aggregate hundreds of millions of in-dividual voter file records and isolate subgroups that scholars have hypothesized will beadversely impacted by Voter ID statutes. The difference-in-differences approach demon-strates that Voter ID policies can reduce turnout among the young, the poor and amongindividuals who move frequently. This study presents a template for future scholars toexamine heterogeneous treatment effects caused by state level interventions.

More research needs to be done on the subject. I qualify my conclusions for the followingreasons. First, the results are dependent on a relatively small number of states that modifiedtheir election law policies. Second, many of the strictest Voter ID laws have been passedin the last year, and future scholars will need to examine their effects. We will have amore definitive answer to this research question in coming years, after current Voter IDlaws have been in effect for a longer duration and after strict Voter ID laws take effect in aseries of additional states. Third, while this powerful, data source enables me to aggregatemillions of individual level records, it is not without error.

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