Citizens unequally participate in referendums, and this may systematically bias policy in favor of those who vote. Some view compulsory voting as an important tool to alleviate this problem, whereas others worry about its detrimental effects on the legitimacy and quality of democratic decision making. So far, however, we lack systematic knowledge about the causal effect of compulsory voting on public policy. We argue that sanctioned compulsory voting mobilizes citizens at the bottom of the income distribution and that this translates into an increase in support for leftist policies. We empirically explore the effects of a sanctioned compulsory voting law on direct‐democratic decision making in Switzerland. We find that compulsory voting significantly increases electoral support for leftist policy positions in referendums by up to 20 percentage points. We discuss the implications of these results for our understanding of the policy consequences of electoral institutions.

Replication Materials The data, code, and any additional materials required to replicate all analyses in this article are available on the American Journal of Political Science Dataverse within the Harvard Dataverse Network, at: http://dx.doi.org/10.7910/DVN/29591.

One of the fundamental objectives of democracy is to ensure that public policy responds to citizens' needs. A large literature has demonstrated, however, that there exist significant differences in civic engagement across politically relevant, sociodemographic divides: Low income earners, the less educated, the less urban, the young, and those belonging to ethnic minorities have a significantly lower propensity to vote (Armingeon and Schädel 2015; Kasara and Suryanarayan 2015; Mueller and Stratmann 2003; Nevitte et al. 2009; Verba, Schlozman, and Brady 1995).1 From this perspective, low turnout may reduce or even destroy the positive welfare effects of government responsiveness through electoral accountability (Björkman and Svensson 2009; Strömberg 2004), a phenomenon that Lijphart (1997) has called the “democratic dilemma.” To the extent that public policy systematically benefits voters over nonvoters, those who abstain may “become locked into a self‐fulfilling cycle of quiescence, alienation and government neglect” (Hill 2006, 216). To preserve the welfare‐enhancing effect of electoral accountability, Lijphart (1997) and others (Dahl 1989; Hill 2006) have pointed out that compulsory voting may reduce representational inequality by mobilizing those citizens who would otherwise remain politically inactive. This incentivizes policy makers to enact policies that better serve the needs of those who had previously been underrepresented. Others, however, worry that compulsory voting reduces the quality of electoral choice and creates inefficiencies because sociodemographic turnout differences may simply reflect differences in affectedness or information (Feddersen and Pesendorfer 1999; Saunders 2011). For example, compulsory voting could increase the share of less informed voters, which may reduce the quality of electoral choice. Moreover, to the extent that compulsory voting remains inconsequential for electoral outcomes, low turnout would actually be preferable from an efficiency perspective. So far, there exists overwhelming evidence that turnout in elections tends to be higher in countries that practice compulsory voting (Jackman 2001; Mueller and Stratmann 2003) and that turnout affects the distribution of votes across parties and candidates (Brunell and DiNardo 2004; Citrin, Schickler, and Sides 2003; Hansford and Gomez 2010; Kohler and Rose 2010). Some have found that turnout tends to benefit the Democrats in the United States (Citrin, Schickler, and Sides 2003; Erikson 1995) and the Labor Party in Australia (Fowler 2013). Others document that the Republican Party realizes higher vote shares in high‐turnout elections (Nagel and McNulty 1996; Tucker, Vedlitz, and DeNardo 1986). This previous work has provided insights into the effects of turnout on elections in which parties and candidates offer entire packages of multidimensional policy bundles. So far, however, we lack knowledge about how turnout affects direct‐democratic policy decisions. We explore the public policy effects of turnout by examining how sanctioned compulsory voting affects referendum outcomes. We argue that imposing a fine for abstention increases turnout among those at the bottom of the income distribution. This is because a monetary sanction imposes the highest relative costs on those who have the least financial resources available, and, as is well documented in the literature, low‐income individuals generally have a low probability of participating in elections under voluntary voting (Filer, Kenny, and Morton 1991; Husted and Kenny 1997). Thus, the set of citizens who can be mobilized by electoral institutions such as compulsory voting is particularly large. Since low‐income voters favor more redistribution than high‐income individuals (Alesina and La Ferrara 2005; Lipset 1959; Meltzer and Richard 1981), differential mobilization should result in more electoral support for leftist policies, that is, policies that aim to lower income inequality, increase welfare spending, enhance workers' employment conditions, and strengthen pension systems (Kenworthy and Pontusson 2005; Mahler 2008; Mueller and Stratmann 2003). Our evidence is based on an analysis of direct legislation in Switzerland and consists of two parts. The first and major part is a causal evaluation of the effects of sanctioned compulsory voting in the Swiss canton Vaud. This analysis enables us to estimate the causal effect of compulsory voting on leftist policy support in referendums. The second component of our empirical evidence is a correlational study of the relationship between compulsory voting and support for leftist policy proposals in referendums in all Swiss cantons from 1908 to 1970, which allows us to explore the generalizability of our main findings. We first estimate the effects of a sanctioned compulsory voting law in the Swiss canton Vaud that aimed to mobilize citizens to participate in direct legislation. Vaud practiced compulsory voting for more than 20 years (1925–48). Abstention triggered a fine that local police authorities collected by visiting nonvoters' homes in person. Such a focus on federal referendum outcomes in one out of many cantons in a multilevel system provides us with a design in which it is plausible to assume that federal referendum issues are exogenous to policy preferences within this single subnational jurisdiction (Bechtel 2012). This circumvents some of the methodological issues that arise when examining national election outcomes where parties' and candidates' policy positions tend to form endogenously. Moreover, studying this period promises insights into the role of electoral institutions and political participation for the evolution of the welfare state: In many of the federal referendums, citizens voted on the fundamental components of the modern welfare state, such as income taxation, the health system, the right to work, pension schemes, and job security regulations (Emmenegger 2009; Linder 1994). The results of our study of federal referendum outcomes in Vaud suggest that sanctioned compulsory voting has a massive effect on turnout, increasing participation in direct legislation by almost 30 percentage points, which implies that turnout was close to universal. Moreover, we find that this massive turnout differentially strengthens electoral support for leftist policy positions by about 80% over the baseline level. These results remain robust when using different model specifications, applying permutation tests, and employing multi‐way clustered standard errors. Based on our findings, we also report point predictions for important welfare and social policy proposals of the left. The results suggest that compulsory voting also had a considerable impact on support for specific referendums on important redistributive policy issues. We then explore the external validity of our main findings by analyzing referendums in all Swiss cantons from 1908 to 1970. These correlational results suggest that our estimates generalize to other cantons and time periods. These findings speak to several literatures that have explored the policy impact of political participation and, more generally, the effects of electoral institutions on public policy. First, most scholars agree that knowledge about the political consequences of virtually universal turnout is crucial to our evaluation of the potential biases in public policy due to unequal political participation. Yet previous work has either examined the impact of relatively moderate increases in turnout (Filer, Kenny, and Morton 1993; Hansford and Gomez 2010; Knack 1994) or relied on stated preferences of nonvoters in surveys to explore this issue (Selb and Lachat 2009). Although these studies have generated important insights, their ability to explore the actual policy effects of compulsory voting remains limited. Already Lijphart (1997, 4) points out that “nonvoters who are asked their opinions on policy and partisan preferences in surveys are typically citizens who have not given these questions much thought, who have not been politically mobilized, and who, in terms of social class, have not developed class consciousness. It is highly likely that, if they were mobilized to vote, their votes would be quite different from their responses in opinion polls.” Finally, our results also add to an ongoing debate about how compulsory voting may or may not affect political stability (Jackman 2001; Lijphart 1997) and inform the literature on the consequences of electoral institutions for the rise of the political left (Boix 1999; Rokkan 1970) and the evolution of the modern welfare state (Husted and Kenny 1997; Radcliff 1992). We elaborate on the implications of our findings in more detail in the conclusion.

Compulsory Voting, Differential Mobilization, and Public Policy Previous Work Several scholars have argued that high levels of turnout are desirable because they increase the legitimacy and the stability of the political system (Dahl 1989; Lijphart 1997; Saunders 2011). This debate has stimulated a large empirical literature that has examined the effects of compulsory voting on political participation and political interest along with the social, economic, and political determinants of turnout. Most studies have focused on estimating the mobilization effects of compulsory voting (Jackman 2001; Panagopoulos 2011). Countries that practice compulsory voting experience turnout levels that are 7 to 15 percentage points higher on average than in countries where voting is voluntary (Jackman 1987; Mueller and Stratmann 2003). Recent estimates based on subnational evidence in combination with causal inference techniques suggest that these contemporaneous mobilization effects may be even larger (Bechtel, Hangartner, and Schmid 2015). Scholarship has also examined the effects of compulsory voting and turnout on elections by examining changes in parties' or candidates' vote shares. While earlier studies report somewhat mixed results (Nagel and McNulty 1996; Tucker, Vedlitz, and DeNardo 1986), the most recent set of studies documents that high turnout improves the representation of Latinos and Asian Americans in U.S. city elections (Hajnal and Trounstine 2005), increases vote shares of mainstream parties (Ferwerda 2014), and raises electoral support for the Democrats in the United States (Citrin, Schickler, and Sides 2003; Hansford and Gomez 2010). In the study that is most closely related to our own contribution, Fowler (2013) shows that higher turnout due to compulsory voting increases vote shares for the Labor Party in Australian state assembly elections. This previous work suggests that turnout matters for the outcomes of elections in which parties and candidates compete for office. We advance the literature by studying the effects of compulsory voting on the outcomes of referendums in which citizens directly vote on policy issues. Mobilization, Sanctioned Compulsory Voting, and Public Policy How do increases in political participation affect policy choices in referendums? We answer this question by focusing on compulsory voting as a legal intervention that aims to increase political participation by (exogenously) changing the costs of voting. Other examples could be the introduction of postal voting, the removal of poll taxes, weather events, changes in the accessibility of polling stations, or the introduction of literacy tests. These instruments and their introduction are typically independent of the dominant policy issues in pre‐election periods, the specific content of referendums, the quality of the candidates who run for office, parties' campaign strategies, or targeted campaign messages by political interest groups. Increases in the costs of voting will demobilize citizens to participate in elections, whereas increases in the costs of abstaining will mobilize individuals (Riker and Ordeshook 1968). But if all citizens equally respond to the cost changes, their interests would still be equally well (or poorly) represented. Thus, according to the equal mobilization argument, changes in the costs of voting or nonvoting will remain inconsequential for public policy.2 Our theory starts from the assumption that citizens have heterogeneous propensities to vote. Any theoretical prediction about the effects of changes in the costs of nonvoting on turnout depends on how these individual propensities respond to cost shocks. In principle, it might be possible that individuals respond uniformly to changes in the costs of nonvoting. This would result in an equal mobilization of different voter groups. The available empirical evidence, however, suggests that citizens do not respond uniformly to changes in voting costs. Rather, the turnout effects of mobilization instruments appear to depend on their specific nature (Jackman 2001). For example, literacy tests impose particularly high costs on less educated citizens. As a consequence, such tests depress turnout among those with low levels of education (Filer, Kenny, and Morton 1993). We focus on two specific arguments about the effects of mobilization efforts on public policy: the amplifying bias argument and the bias correction argument. Both theories reject the view that shocks to the costs of voting have equal mobilization effects, albeit in opposite directions. The amplifying bias argument predicts that nonpartisan mobilization efforts such as simple get‐out‐the‐vote campaigns or norm‐based approaches such as compulsory voting will increase representational inequality because they are most effective among those who already have a high propensity to vote.3 Therefore, increases in turnout will translate into more representational inequality, which will amplify biases in public policy. Recent field experimental evidence supports this idea: Enos, Fowler, and Vavreck (2014) show that get‐out‐the‐vote interventions more strongly mobilize those who already have a high propensity to vote, which would further increase the potential biases in policy decisions due to unequal political participation. Since constituencies that support right‐wing policies have a higher propensity to vote (Enos, Fowler, and Vavreck 2014), this reasoning suggests that compulsory voting will strengthen electoral support for right‐wing policies more strongly than support for leftist policies. In contrast, we argue that increasing civic engagement can decrease representational inequality and thereby reduce policy biases. This bias correction argument holds that introducing fines for nonvoting places a disproportionate burden on those with low incomes, who have been documented to have a particularly low probability of turning out (Fowler 2013; Mueller and Stratmann 2003; Verba, Schlozman, and Brady 1995). Such a reasoning is consistent with the finding that poll taxes, which impose higher relative costs on low earners, indeed reduce turnout more strongly in poorer counties (Filer, Kenny, and Morton 1991). Since a monetary punishment for nonvoting will more strongly mobilize low‐income individuals, this will add voters located at the lower end of the income distribution to the electorate. Following Meltzer and Richard (1981), this changes the median voter's preferred level of redistribution: The median voter under sanctioned compulsory voting will demand more redistribution than the median voter under voluntary voting. Thus, compulsory voting will increase demand for redistributive policy instruments such as social welfare, pension systems, and universal health care.4 Therefore, the bias correction argument predicts an increase in turnout among low‐income voters that translates into a shift toward more support for leftist, redistributive policies (Husted and Kenny 1997). We examine the empirical validity of our argument by studying the policy impact of sanctioned compulsory voting in Switzerland in the first half of the 20th century. Switzerland has a direct‐democratic system where citizens directly vote on policy issues in referendums. This allows us to estimate how turnout changes due to compulsory voting affect direct‐democratic policy choices. Therefore, our study promises to provide evidence that enables us to arbitrate between different theoretical accounts of the effects of turnout on policy decisions in referendums.

The Swiss Party System and Compulsory Voting in Vaud in the Early 20th Century Switzerland offers a useful political system for studying the policy effects of compulsory voting in referendums. Already Lijphart (1997) emphasizes its exceptionally low levels of turnout, and Linder (1994, 95–96) observes that “especially when participation is low, the choir of Swiss direct democracy sings in upper or middle‐class tones.” Moreover, the period we study (1908–70) includes the advent of industrialization in the early 20th century that marked the rise of the classic left‐right conflict between capital and labor interests in Switzerland, and this cleavage continued to dominate political competition for decades (Fueter 1928; Kreis 2014). The increasing importance of the industrial sector and the economic consequences of World War I further strengthened the support of the working class for the Social Democratic Party (SP). Catering to their low‐income constituencies, the SP demanded leftist policies, such as social benefits, a tax‐funded pension system, public health care, and other types of redistributive policies (Linder 1994). In contrast, the Free Democratic Party (FDP) wanted to prevent state interventions in the economy and opposed welfare programs. Since the FDP held the majority of seats in the federal parliament, the SP could influence public policy only through direct‐democratic decision making. As a consequence, citizens had to vote on important welfare and social policy proposals in federal referendums. Prominent examples include proposals to introduce a public pension system and a public disability insurance (1925, 1947), a popular initiative to fight the economic crisis (1935), and a popular initiative for economic reforms and the establishment of a right to work (1947). Within less than three decades, direct legislation on economic and social policy formed the basis of the modern welfare state in Switzerland. To provide a causal estimate of how turnout affects public policy, we first analyze the effects of sanctioned compulsory voting that the canton of Vaud introduced in November 1924. According to Vaud's compulsory voting law, all citizens between 20 and 65 years had to participate in federal referendums. To assess whether the introduction of compulsory voting constitutes an exogenous intervention, we searched the cantonal archives and carefully reviewed a large set of primary documents, including parliamentary minutes and newspapers. These sources suggest that policy makers in Vaud tried to increase political participation and interest in political matters and to ensure that outcomes of federal referendums in Vaud had a stronger impact on federal legislative decisions (Bulletin du Grand Conseil 1924, 658). We also analyzed the parliamentary minutes to explore whether policy makers introduced compulsory voting strategically. In particular, one may worry that the SP advocated compulsory voting because it expected to benefit from higher support for leftist policy positions. The archival material, however, does not support this hypothesis. First, the parliamentary minutes suggest that policy makers lacked evidence on the effects of sanctioned compulsory voting. They explicitly viewed the introduction of compulsory voting for federal referendums as an experiment to learn about its impact on civic engagement (Bulletin du Grand Conseil 1924, 705–7). Second, the SP did not hold a majority of seats in Vaud's parliament, which means that it was unable to introduce compulsory voting on its own. Third, the SP actually opposed sanctioned compulsory voting because of the fear that this may exacerbate Switzerland's internal division between French‐ and German‐speaking regions (Bulletin du Grand Conseil 1924, 710–11). Fourth, it expected that the enforcement of sanctioned compulsory voting would cause overly high administrative costs and confusion among voters about which types of referendums and elections would be compulsory and which would remain voluntary (Bulletin du Grand Conseil 1924, 703–5). Finally, the SP was concerned that the considerable fine for nonvoting would infuriate their voter base, which consisted mainly of low‐income individuals. At the end of the parliamentary debate, the FDP, which wanted to increase the weight of the French‐speaking cantons in federal direct legislation to prevent further centralization decisions that would have strengthened the federal state, supported the introduction of compulsory voting, whereas the SP opposed it. Since the FDP held the majority of seats (54%) in Vaud's cantonal parliament, it introduced compulsory voting as part of a revision of the law on political rights #113/49 on November 17, 1924. In sum, it appears implausible to assume that the SP strategically introduced compulsory voting because it expected to benefit from it. This lends plausibility to the idea of compulsory voting as an exogenous policy intervention.5 Vaud's compulsory voting law sanctioned nonvoters by imposing a fine of two Swiss francs (Gazette de Lausanne 1924). This amount appears substantial, as it equaled about 125% of a low‐skilled worker's hourly wage (Siegenthaler and Ritzmann 1996). Local police authorities collected the fine by visiting nonvoters' homes in person. The revenues from the fine, which varied from 8,000 to 16,000 Swiss francs per referendum, helped finance a charity fund for poor people and public hospitals.6 Vaud temporarily suspended its compulsory voting law in the World War II period from 1940 to 1945 and reactivated it in late 1945 (Gazette de Lausanne 1945). Although Vaud's government continued to generally support compulsory voting, it was eventually abolished in 1948 because of its high administrative costs.

Data and Method Dependent Variables For the treated and control districts, we collected data on Turnout in all conflictual federal referendums (21) held from 1908 to 1948 together with information about the outcomes of these direct‐democratic decisions. We define a referendum as conflictual if the two major parties, the FDP and the SP, offered diverging endorsements (e.g., if the FDP recommended voting in favor of a proposal while the SP recommended voting against it). Table 6 in the supporting information provides a list of all referendums included in our sample together with information about turnout and yes/no vote shares. Examining these referendum results provides us with a direct measure of support for a specific policy issue. In contrast, the use of a party's vote share would not allow us to disentangle whether changes in electoral support are truly due to compulsory voting or merely the result of parties strategically adjusting their policy platforms and pools of candidates in response to the newly mobilized voters. By examining votes on specific policy issues, we circumvent this hindrance to providing a causal estimate of the public policy effects of compulsory voting. Support Left, which measures the share of votes for a proposal if it is endorsed by the Social Democratic Party and the share of votes against a proposal if the SP recommends voting against the proposal. In the robustness section, we explore the sensitivity of our results to an alternative, manual coding of proposals that does not rely on parties' endorsements. The results remain very similar.Support Left as (1) and is the number of yes and no votes, respectively, and denotes the number of eligible voters. The proposal‐specific indicator variable SP equals 1 if the proposal was endorsed by the SP and is 0 if the SP opposed the proposal. To explore the effects of compulsory voting on support for leftist/rightist policies, we need measures of electoral support for policy proposals endorsed by the left. We create the variable, which measures the share of votes for a proposal if it is endorsed by the Social Democratic Party and the share of votes against a proposal if the SP recommends voting against the proposal. In the robustness section, we explore the sensitivity of our results to an alternative, manual coding of proposals that does not rely on parties' endorsements. The results remain very similar. 7 More formally, we defineaswhereandis the number of yes and no votes, respectively, anddenotes the number of eligible voters. The proposal‐specific indicator variableequals 1 if the proposal was endorsed by the SP and is 0 if the SP opposed the proposal. Support Right to measure support for rightist policy proposals, defined as (2) and is the number of yes and no votes, respectively, and denotes the number of eligible voters. The proposal‐specific indicator variable FDP equals 1 if the proposal was endorsed by the FDP and is 0 if the FDP opposed the proposal. Analogously, we create the variableto measure support for rightist policy proposals, defined aswhereandis the number of yes and no votes, respectively, anddenotes the number of eligible voters. The proposal‐specific indicator variableequals 1 if the proposal was endorsed by the FDP and is 0 if the FDP opposed the proposal. 8 Relative Support Left. This variable measures the share of yes votes as a share of the total number of valid votes if the SP endorses the proposal and the share of no votes as a share of the total number of valid votes if the SP opposes the proposal. Thus, this variable directly measures relative electoral support for policy positions of the left. Formally, the variable is defined as (3) Finally, to allow for a direct statistical test of the relative effect of changes in turnout on electoral support, we construct the variable. This variable measures the share of yes votes as a share of the total number of valid votes if the SP endorses the proposal and the share of no votes as a share of the total number of valid votes if the SP opposes the proposal. Thus, this variable directly measures relative electoral support for policy positions of the left. Formally, the variable is defined as We collect a large set of covariates that previous work has shown to help predict turnout and election outcomes. These data include the number of ballots in a referendum, public spending and revenues, percentage of secondary students, share of urban population, and share of people older than 50 or 60, respectively. Since economic indicators are only available since 1998, we use the number of motor vehicles per person as a proxy for economic performance (Duch and Stevenson 2010; Filer, Kenny, and Morton 1993; Knack 1995). Table 4 in the supporting information provides a complete covariate list and data sources. Research Design We estimate the causal effect of compulsory voting on turnout and support for leftist/rightist policy proposals in federal referendums. Ideally, we would compare district‐level outcomes of federal referendums under voluntary voting with referendum outcomes in the same districts under compulsory voting. However, we never observe both outcomes for the same districts. Therefore, we need to impute a credible counterfactual that serves as the baseline when estimating a causal effect. A simple before‐and‐after comparison of treated districts will fall short of providing convincing causal estimates, as many time‐varying factors may be responsible for differences in the outcome variables over time. For example, citizens voted on very different policy proposals in these periods, which would already undermine the credibility of such a before‐and‐after comparison. To estimate the causal effect of compulsory voting on support for leftist policy, we employ standard fixed effects regression. The idea is to impute the missing counterfactual—that is, the change in electoral support for a specific policy proposal we would expect in the treated districts in the absence of compulsory voting—using the change in electoral support for the same policy proposals in comparable control districts that did not practice compulsory voting. This design allows us to identify the causal effect in the presence of unobservable time‐invariant or smoothly changing confounders. It requires, however, that we exclude districts in which voting was compulsory at some point in the period we study. Figure 2 in the supporting information shows a map of Switzerland in the early 20th century that identifies which cantons are included in the analysis as control units. We estimate the effect of compulsory voting on policy support using fixed effects regressions, as this identifies our quantity of interest solely on the basis of within‐district variation in treatment, turnout, and referendum outcomes. The fixed effects estimator for panel data, a generalization of the difference‐in‐difference design to multiple time periods, provides us with a valid causal estimate under the parallel trends assumption, as stated in Equation (5) in Section I in the supporting information (Angrist and Pischke 2008). The parallel trends assumption says that in the absence of compulsory voting, the dependent variable (e.g., turnout) would have experienced the same changes over time as in the control districts in which voting remained voluntary during the treatment period. Further below we show that the parallel trends assumption is plausible in our application. Therefore, this identification strategy prevents unobserved, time‐invariant district characteristics, such as a district's geographic features, its local political culture, or its demographic, economic, and social composition, from confounding our causal effect (see Section I in the supporting information for a detailed, formal treatment of our research design). Furthermore, including district‐specific time trends helps to account for local trends in unobserved confounders, such as changes in voter preferences. Several features of our research design suggest the use of two‐way clustered standard errors to avoid falsely rejecting the null hypothesis of no effect (Bertrand, Duflo, and Mullainathan 2004). More specifically, since we observe the same districts over time and all districts vote on the same referendum on the same day, we have to account for intradistrict and contemporaneous dependence. Although this does not affect the estimated treatment effect, which will remain unbiased, throughout all estimations we compute standard errors that use the two‐way variance estimator proposed by Cameron, Gelbach, and Miller (2011), which provides us with standard errors that are robust against both potential district‐level and referendum‐level dependencies. We also address the fact that our treatment is imposed at the cantonal level, as this means that the treated districts within a canton are not independent in case of a common cantonal‐level shock. Although, again, this does not affect the magnitude of the estimated treatment effect, this may result in deflated standard errors. To address this issue, we compute the p‐values using the two‐way clustered standard errors in combination with a t‐distribution with only 10 degrees of freedom. This reflects that, although we have 12 cantons in our sample, the intervention was imposed at the cantonal level, and, additionally, one of our covariates (share of automobiles) is measured at the cantonal level.

Results Compulsory Voting, Turnout, and Support for Leftist Policy in Referendums Model 1 in Table 1 presents fixed effects regression estimates of the impact of compulsory voting on turnout for federal referendums. We focus on referendums in which the two major parties offered conflictual endorsements; that is, one of the parties recommended voting for a policy, whereas the other party advocated voting against the proposal.9 All models include district and referendum fixed effects. We also include district‐specific linear time trends to account for smooth, time‐varying trends at the district level and a full set of sociodemographic and economic covariates.10 All estimations use two‐way robust standard errors that are clustered by district and referendum day (Cameron, Gelbach, and Miller 2011). Additionally, for our treatment estimate, we report p‐values that are based on the t‐distribution with 10 degrees of freedom to account for the fact that the treatment is applied at the cantonal level. We report various robustness as well as placebo tests further below. According to Model 1 in Table 1, turnout for referendums increases significantly (p <.01), by 33 percentage points on average in the period in which Vaud practiced compulsory voting. To better grasp the magnitude of this effect, we divide the point estimate by the counterfactual turnout level in the absence of compulsory voting. We find that compulsory voting boosts turnout by 66% on average. Table 1. The Policy Effects of Compulsory Voting Model Outcome (1) Turnout (2) Support Left (3) Support Right (4) Rel. Support Left Mean in treated VD 0.83 0.35 0.48 0.42 Compulsory voting 0.33 0.23 0.10 0.19 (6.44) (3.56) (1.68) (2.30) [0.00] [0.01] [0.12] [0.04] Observations 2,163 2,163 2,163 2,163 Districts 103 103 103 103 District FEs ✓ ✓ ✓ ✓ Referendum Day FEs ✓ ✓ ✓ ✓ District time trends ✓ ✓ ✓ ✓ Covariates ✓ ✓ ✓ ✓ Effect size (% Δ) 66% 192% 26% 83% How does this pronounced increase in political participation affect support for leftist and rightist policy in referendums? Model 2 reports our results for the variable Support Left. This dependent variable measures the share of votes for proposals endorsed by the SP and the share of votes against a proposal if the SP recommended voting against the policy (see Equation 1). Put simply, this captures support for the position advocated by the left party. We again include our compulsory voting treatment indicator along with a full set of sociodemographic and economic covariates, district fixed effects, referendum fixed effects, and district‐specific linear time trends. The results suggest that electoral support for leftist policy positions increases significantly, by 23 percentage points in the period in which Vaud sanctioned nonvoters. This represents a significant (p = .01) increase of more than 190% over the baseline level of support for leftist policy positions in the absence of compulsory voting. According to the equal mobilization argument, compulsory voting should also have mobilized support for rightist policies. To evaluate this prediction, we estimate the effect of compulsory voting on the variable Support Right. This variable measures the share of votes for proposals that the FDP endorsed and the share of votes against a proposal if the SP recommended voting against the policy (see Equation 2). Model 3 in Table 1 reports the results. The coefficient on our treatment indicator is positive (.10) but only half the size of the effect we find for leftist policy. Moreover, the effect on Support Right is not significant if we use the p‐values for a t‐distribution with 10 degrees of freedom (p = .12). These results suggest that leftist policy positions gained more electoral support due to compulsory voting. Yet we still lack a direct test of the relative effect of compulsory voting on referendums. To implement such a test and directly estimate the differential mobilization effect of compulsory voting, we regress the variable Relative Support Left on the treatment indicator. This variable measures the relative strength of support for leftist policy proposals. If a proposal was endorsed by the SP, the variable equals the number of yes votes as a share of the total number of valid votes for the proposal. In case a proposal was opposed by the SP, the variable equals the share of no votes as a share of the total number of valid votes. Model 4 in Table 1 reports our estimate. We find that compulsory voting significantly (p = .04) increases relative support for leftist policy positions, by 19 percentage points on average. Compared to the counterfactual level of Relative Support Left, this constitutes an increase by 80%. Thus, the turnout increase due to compulsory voting strongly boosts electoral support for leftist policies even when taking into account that it may also have some mobilization effects on voters of the right. What mechanism underlies this differential mobilization effect? We theorize that parties engage in an efficient allocation of their scarce campaign resources and invest most strongly in mobilization efforts in the context of referendums on core issues as opposed to votes on peripheral issues. An efficiency‐based allocation of campaign resources has direct consequences for a party's mobilization efforts and the potential effect of compulsory voting. Parties will mobilize more strongly and successfully when citizens can vote on core issues as compared to peripheral issues that have a lower priority on their policy agenda. This reasoning implies that, although compulsory voting generally increases support for leftist policies, it will most strongly mobilize voters in referendums on noncore issues because parties spend their resources on maximizing support for core issues. Thus, the effect of compulsory voting on turnout and support for leftist policies should be greater when the referendum is on peripheral issues than when voters decide on core issues where parties have already heavily mobilized. To evaluate this prediction, we performed a qualitative coding of all referendums to identify those proposals that concerned core issues of the left. These are decisions on unemployment benefits, pensions, the size of government, social welfare, labor rights, the minimum wage, and immigration. We use this information to partition the data and reestimate the main models on these two subsamples. Table 2 reports the results. First, we note that the effect of compulsory voting on turnout is significant and sizable for both core and noncore issues. However, we find that for noncore issues, the effect of compulsory voting on turnout is greater (41 percentage points) than for core issues (26 percentage points), although the mean turnout in Vaud under compulsory voting is quite similar (85% and 82%). This suggests that compulsory voting has the strongest effect on turnout when parties tend to mobilize less and is consistent with the idea of parties engaging in an efficient allocation of their scarce campaign resources. Consequently, when parties' campaign efforts succeed in realizing almost the full potential of electoral support for a policy, compulsory voting itself has less pronounced effects. Table 2. The Policy Effects of Compulsory Voting on Core Issues of the Left (1) (2) (3) (4) (5) (6) (7) (8) Model Outcome Turnout Support Left Support Right Rel. Support Left Core issue left No Yes No Yes No Yes No Yes Mean in treated VD 0.85 0.82 0.43 0.29 0.42 0.53 0.50 0.36 Compulsory voting 0.41 0.26 0.41 0.15 0.00 0.10 0.37 0.11 (3.55) (7.02) (3.09) (3.79) (0.01) (1.89) (2.63) (1.79) [0.01] [0.00] [0.01] [0.00] [0.99] [0.09] [0.03] [0.10] Observations 1,545 1,545 1,545 1,545 1,545 1,545 1,545 1,545 Districts 103 103 103 103 103 103 103 103 District FEs ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ Referendum Day FEs ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ District time trends ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ Covariates ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ Effect size (% Δ) 93% 46% 2050% 107% 0% 23% 285% 44% The remaining results in Table 2 underscore this impression. The effect of compulsory voting is considerably stronger for referendums on noncore issues. When considering Support Left (Model 3), the treatment effect for peripheral issues is estimated at 41 percentage points, whereas the effect for core issues (Model 4) is considerably smaller (15 percentage points). We also reestimate the main model for Relative Support Left (Models 7 and 8). Although compulsory voting still increases electoral support for leftist policies, this differential mobilization effect is more pronounced when examining referendums on policy proposals that do not represent core issues of the left (the estimated treatment effect is 37 percentage points for noncore issues and 11 percentage points for core issues of the left). Taken together, our results suggest that, although compulsory voting affects electoral support significantly for both peripheral and core issues, the effect materializes most strongly in referendums on less ideologically defining issues. These estimates provide information about average treatment effects. But what did the effects of compulsory voting look like in specific and politically important referendums? To illustrate the impact of the surge in turnout, we compute its effects on three policy proposals particularly relevant from the perspective of the left‐right welfare state cleavage. The first referendum is the so‐called “crisis initiative” in 1935, a popular initiative to fight the economic crisis. The initiative stipulated a large set of leftist policy reforms, including a state guarantee for a minimum wage, subsidies to workers and farmers, higher unemployment benefits, stricter regulation of financial markets, restrictions on capital outflows, and stricter antitrust regulation. Based on our estimates, compulsory voting increased support for the crisis initiative in Vaud by 22 percentage points as compared to the counterfactual level of support in the absence of compulsory voting. As another example, consider the popular initiative to introduce the right to work in 1947. According to our findings, electoral support for this policy was 30 percentage points higher in Vaud than it would have been without compulsory voting. Clearly, political power also implies the ability to prevent policy changes advocated by political opponents. Therefore, as a final example, we have computed the effect of compulsory voting on electoral support for a federal bill that would have reduced public officials' salaries in the context of the economic crisis in 1933. The SP opposed this bill, and we find that compulsory voting reduced support for this proposal by 15 percentage points due to the mobilization effect of compulsory voting. Identifying Assumption and Robustness In this section, we first demonstrate the plausibility of the main assumption needed for estimating the causal effect of compulsory voting on turnout and public policy. We then turn to probing the robustness of our results. We relax some of the assumptions about the functional form that underlies our estimates, perform permutation tests to further explore the significance of our findings, and reestimate the main results using an alternative, manual coding of leftist policy proposals. Parallel Trends Assumption To assess the plausibility of our identifying assumption, we consider the evolution of all four of our outcome variables in treated and control districts in the pretreatment period. This constitutes an important step to assess whether the outcome variables in treated and control districts followed parallel trends prior to the introduction of compulsory voting. If this is the case, it adds to the credibility of our results because it is more plausible to assume that, in the absence of the introduction of compulsory voting, our outcome variables in treated and control districts would have followed parallel trends. The upper left panel in Figure 1 plots average turnout in conflictual referendums by treatment group. In the period prior to compulsory voting, turnout trends are almost perfectly similar in both treated and control districts. This does not constitute a direct test of the parallel trends assumption, which remains fundamentally untestable. Yet the parallelism of pretreatment trends lends credibility to the assumption that in the absence of compulsory voting, treated and control districts would have followed the same turnout trajectory. As soon as Vaud introduces compulsory voting, however, the two time series strongly diverge. Thus, the turnout effect we document above is also clearly visible to the naked eye. Figure 1 Open in figure viewer PowerPoint Pretreatment Trends in Turnout and Support for Leftist/Rightist Policy Positions in Federal ReferendumsNote: The figure shows pretreatment trends (period averages) for our four outcome variables (Turnout, Support Left, Support Right, and Relative Support Left) in Vaud and the control districts (in %). DiD = difference‐in‐differences. The pretreatment period ends in 1924. Vaud introduced compulsory voting in 1925. We also examine the pretreatment trends in support for leftist and rightist policy proposals. The upper right panel in Figure 1 shows the evolution of support for proposals endorsed by the SP in treated and control districts over time. In the pretreatment period, electoral support for policies endorsed by the Social Democratic Party evolve similarly in both treated and control districts. But once compulsory voting is introduced, support for leftist policy increases in treated districts and remains virtually constant in the control district. The lower left panel in Figure 1 shows the pretreatment trends in support for proposals endorsed by the right. Support for proposals endorsed by the FDP follow very similar trends in treated and control districts prior to the introduction of compulsory voting. The lower right panel in Figure 1 plots relative support for leftist policy proposals, our main outcome variable. We again find that prior to the introduction of compulsory voting, support for leftist policy relative to right policy proposals trended downward in both groups, and the change seems almost identical. Taken together, these results strengthen our confidence in the identifying assumption: It appears reasonable to assume that in the absence of compulsory voting, our outcomes of interest would have followed similar trends. Therefore, when examining the effects in the treatment period, observable changes in the dependent variables in the control districts provide us with a credible counterfactual change in turnout and policy support in the treated districts. Functional‐Form Assumptions We conduct several tests to explore the robustness of our results. First, we reestimate all models and additionally include district‐specific quadratic time trends. This functional form relaxes the assumptions needed for estimation since it eliminates nonlinear local trends in unobserved covariates, such as smooth changes in sociodemographics such as economic growth or age structure. As a consequence, this adds to our confidence that the estimated treatment effect can be attributed to the introduction of compulsory voting and not to some trend in unobserved covariates. The results in Table 7 in the supporting information are comparable to those reported in Table 1. Most importantly, we again find that compulsory voting differentially mobilized support for leftist policy proposals: We estimate that, on average, relative support for leftist policy proposals in referendums significantly increased by 17 percentage points due to compulsory voting (p = .06). Second, we reestimate the treatment effects within a fully nonparametric setting by excluding all covariates and time trends. Table 8 in the supporting information shows the results. The treatment effects are slightly smaller but exhibit the same pattern: We find a strong and significant turnout increase (estimated at 25 percentage points) under compulsory voting, and the effect on electoral support is again differential: Relative support for leftist policy increases significantly (p = .04) by about 12 percentage points during compulsory voting, and this effect still constitutes a 40% increase over the mean level of relative support for leftist policy proposals. Finally, we reestimate the main results (Table 1) without weights, that is, assigning equal weight to each district. Table 9 in the supporting information reports the results. The estimates are very similar and, if anything, slightly larger than those from our main analysis. Permutation Tests and Alternative Coding of Leftist Policy Proposals We also conduct a series of permutation tests by estimating placebo treatment effects for the control districts (Abadie, Diamond, and Hainmueller 2010). This permutation test proceeds as follows: We define a placebo treatment group that contains all districts in a canton and pretend that these districts practiced compulsory voting in placebo treatment periods defined as 1925–39 and 1946–48. Note that assigning all districts in a canton to either the placebo treatment or the control condition is important to mirror that the actual treatment is applied at the cantonal level. Based on this assignment, we generate additional temporal variation by including four leads and four lags of the placebo treatment indicators. This provides us with a total of nine placebo treatment period indicators. For each of these indicators, we estimate a regression identical to our main model with district fixed effects, referendum fixed effects, district‐specific linear time trends, and all covariates to compute the placebo treatment effect. We repeat this procedure for all 11 control cantons and plot the distribution of these 99 placebo treatment effects. This provides us with the distribution of the treatment effect under the null hypothesis of no effect and does not rely on any assumption about the correlation structure between the error terms. The upper left panel in Figure 3 in the supporting information plots the frequencies of placebo treatment effects on turnout for the control districts. The mass of the distribution is concentrated at 0 percentage points, and the effects are roughly symmetrically distributed. The red bar in Figure 3 indicates the actual treatment effect for our treated districts estimated in the main analysis (about 30 percentage points). We note that all placebo effects are clearly located to the left of this effect. This suggests that the turnout effect we document can be attributed to the fact that Vaud introduced compulsory voting. When computing the corresponding p‐value, we find that the turnout effect is highly significant (p = .01). We repeat this permutation test for all remaining outcome variables: Support Left (p = .01), Support Right (p = .15), and Relative Support Left (p = .02). As predicted by the bias correction argument, the results suggest that the turnout increase induced by compulsory voting had a significantly positive effect on support for policies advocated by the left, both in absolute and relative terms. The p‐values derived from these permutation tests are very similar and, if anything, even smaller compared to those computed from the two‐way clustered standard errors reported above. Our original coding used parties' endorsements to identify leftist policy proposals, and we focused on those proposals for which we found partisan conflict in the party endorsements. To explore the robustness of our results, we perform an alternative, manual left‐right coding of policy proposals. Table 6 in the supporting information provides a list of all proposals together with information about this alternative classification. Our alternative left‐right coding results in a smaller, more restrictive set of referendums that we can analyze. Table 10 in the supporting information presents the results when we reestimate our main models using our alternative left‐right coding. We again find that compulsory voting increases turnout in these referendums by about 29 percentage points, and this estimate is highly significant ( ). Most importantly and consistent with our main results, Model 4 in Table 10 in the supporting information shows that compulsory voting significantly increases relative support for leftist policy proposals by 10 percentage points. Thus, our findings remain intact when using an alternative coding of leftist policy. External Validity: Evidence from Swiss Cantons, 1908–70 So far, we have examined the effect of compulsory voting on public policy in one canton. This focus allowed us to reduce threats to the internal validity of our estimates that result from case heterogeneity and bias induced by observable and unobservable confounders. We deliberately prioritize internal validity over external validity since we want to avoid trying to generalize an estimate that is internally invalid. However, after having established a credible estimate of how compulsory voting affects support for leftist policy, we now turn to the question of whether our findings have the potential to generalize to other time periods and cases. We performed a detailed coding of the archival material for all districts in all Swiss cantons from 1908 to 1970 and collected information about when exactly and how the districts we excluded from our analysis practiced compulsory voting along with the available covariate information. This data collection effort is time‐consuming and challenging because enforcement of compulsory voting sometimes happened at the municipality level, where archival data are often missing. For some cases, there remains some uncertainty about the extent to which compulsory voting was actually enforced. Consequently, we expect the effects to be smaller because of imperfect enforcement. Moreover, since we have only data since 1908 and most cantons had introduced compulsory voting prior to that year, we point out that identification in the subsequent analysis stems mainly from the abolishment of compulsory voting. According to Model 1 in Table 3, compulsory voting again significantly and positively affects turnout in direct legislation. On average, districts that practice compulsory voting experience 10 percentage points higher turnout in federal referendums. We also find a positive and significant effect on support for leftist policy positions: According to Model 2 in Table 3, yes votes for leftist policy proposals increase by about 7 percentage points in periods of compulsory voting. In contrast, compulsory voting is not significantly associated with changes in support for right policy positions (Model 3). Unsurprisingly, the results in Model 4 in Table 3 suggest that compulsory voting and relative support for leftist policy are positively and significantly correlated. Relative support for leftist policy positions increases by 4 percentage points during periods of compulsory voting, which represents an 11% increase over the baseline. These results based on a sample of all cantons from 1908 to 1970 suggest that our results have the potential to generalize to other cantons and time periods. Table 3. Turnout and Support for Leftist Policy Proposals: All Cantons, 1908–70 Model Outcome (1) Turnout (2) Support Left (3) Support Right (4) Rel. Support Left Mean in treated VD 0.74 0.30 0.44 0.40 Compulsory voting 0.10 0.07 0.03 0.04 (3.40) (3.89) (1.68) (2.08) [0.01] [0.00] [0.12] [0.06] Observations 6,255 6,255 6,255 6,255 Districts 172 172 172 172 District FEs ✓ ✓ ✓ ✓ Referendum Day FEs ✓ ✓ ✓ ✓ District linear time trends ✓ ✓ ✓ ✓ Covariates ✓ ✓ ✓ ✓ Effect size (% Δ) 16% 30% 7% 11%

Conclusion Is there a policy bias due to unequal political participation? Can compulsory voting alleviate this bias? Although this idea has attracted considerable attention in the literature and the potential gravity of the underlying problem is well known, we possess little systematic knowledge about the actual policy effects of compulsory voting. We argue that sanctioned compulsory voting increases support for leftist policies because it imposes the highest costs on citizens at the bottom of the income distribution, who tend to hold leftist policy preferences. We explore the empirical validity of this argument in the context of a direct‐democratic system where citizens directly vote on policy issues in referendums. Our results suggest that sanctioned compulsory voting increases turnout in federal referendums massively, by about 30 percentage points on average. More importantly, we find that this turnout increase has a pronounced positive effect on support for leftist policy proposals: Electoral support for policy proposals endorsed by the Social Democratic Party doubles under compulsory voting. We also conduct a set of simulations to explore the magnitude of these effects in specific important referendums that lie at the heart of the left‐right cleavage. We find that compulsory voting induces profound shifts in votes for leftist policy and stricter market regulation. This policy effect of compulsory voting is lower (but still significant) in referendums on core issues, a finding that appears consistent with the argument that parties concentrate campaign spending on core issues, which limits the potential effect compulsory voting can have on referendum outcomes and, in turn, public policy choices. These results add to several literatures that have examined the economic and social policy effects of electoral institutions, and inform the debate about the impact of electoral mobilization on political stability. First, and most directly, our results suggest that exogenous increases in turnout may indeed increase support for leftist policy. Second, since we examine the effects of compulsory voting on support for leftist policy in the period of industrialization and the Great Depression, one may hypothesize that electoral institutions such as compulsory voting have a role to play in our understanding of the evolution of the modern welfare state that has not yet been appreciated in the literature so far. Third, although our analysis focuses on how turnout affects support for specific policies, we expect the findings to also inform the debate about whether political mobilization leads to more erratic electoral outcomes and unstable political majorities by increasing the share of uninformed voters who tend to vote almost randomly. At least in the case we examine, sanctioning nonvoting leads to a systematic increase in electoral support for leftist policies, which appears difficult to square with the random voting argument. We have studied the consequences of turnout in a direct democracy with a focus on estimating an internally valid causal effect. Do our results have the potential to generalize to elections in representative (indirect) democracies? First, we note that the recent evidence on the positive effect of turnout on leftist parties' vote shares in elections is consistent with our findings. Second, however, we acknowledge that the extent to which our results generalize depends on various conditions, such as the importance of valence factors versus issue positions in electoral choices. The generalizability of our results, of course, also hinges on the baseline level of turnout in a political system since low turnout under voluntary voting constitutes a necessary condition for the pronounced effects we document. However, participation rates have been decreasing for decades in most industrialized democracies (Dalton and Wattenberg 2000) and remain far from universal. In the United States, for example, average turnout in presidential elections has remained below 60% since the late 1960s, and in many other countries, participation rates in subnational and European Union elections are even lower. Therefore, our results seem to provide informative evidence for ongoing debates about the desirability of compulsory voting. Third, we have analyzed referendum outcomes (i.e., behavioral data) to learn about the policy effects of compulsory voting. Exploring the causal mechanisms at the individual level would be a valuable endeavor that we leave to subsequent research. Finally, we have examined the effect of a plausibly exogenous change in electoral institutions on policy choices in referendums. Given the potentially profound policy consequences of interventions such as compulsory voting, postal voting, or enfranchisement decisions, future research may want to devote more attention to identifying cases in which we can learn about the effects of political participation on the (strategic) adoption of these and other types of electoral institutions (Drometer and Rincke 2014).

Biographies Michael M. Bechtel is SNSF Research Professor of Political Science, University of St. Gallen, Department of Political Science, Rosenbergstrasse 51, CH‐9000 St. Gallen, Switzerland (mbechtel.mail@gmail.com).

Dominik Hangartner is Associate Professor, London School of Economics and Political Science, Department of Methodology, Houghton Street, London WC2A 2AE, United Kingdom and University of Zurich, Department of Political Science, Affolternstrasse 56, CH‐8050, Zürich, Switzerland (d.hangartner@lse.ac.uk).

Lukas Schmid is Senior Research Associate, University of St. Gallen, Department of Economics, Bodanstrasse 8, CH‐9000 St. Gallen, Switzerland (lukas.schmid@unisg.ch).

Supporting Information Additional Supporting Information may be found in the online version of this article at the publisher's website: Filename Description ajps12224-sup-0001-SupMat.pdf473.4 KB Research Design and Estimation Details Table 4: Variables Description Table 5: Overview of Compulsory Voting in Switzerland Table 6: Overview of Federal Referendums Included in the Analysis Table 7: The Policy Effects of Compulsory Voting: District‐specific Quadratic Time Trends Table 8: The Policy Effects of Compulsory Voting: Fixed‐Effects Only Table 9: Main Results, unweighted Table 10: Turnout and Support for Leftist Policy Proposals: Alternative Coding Table 11: Compulsory Voting Norm in the Swiss Canton of Vaud Figure 2: Switzerland in Early 1900: Treated, Control, and Excluded Cantons Figure 3: Permutation Tests Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

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1 The positive empirical relationship between income and the propensity to vote in industrialized countries has been well documented (DeNardo 1980 1993 2003 2009 1985 1995 1999 2010 2007 2012

2 A related argument holds that citizens who would abstain under voluntary voting would vote randomly under compulsory voting, which would, in expectation, lead to the same prediction.

3 Note that this prediction differs from what we would expect from electoral mobilization by interest groups. For example, recent work argues that unions foster solidarity among their members and thereby strengthen redistributive policy preferences (Mosimann and Pontusson 2015 2006

4 A related literature has examined the correlation between income and voting behavior in elections where citizens vote for parties or candidates. These studies find that the positive correlation between income and vote choice is weaker in richer states (Brooks and Brady 1999 2010 2007 2009

5 In addition, we note that for a clean identification of the average treatment effect on the treated in a difference‐in‐differences design, only the timing of the introduction of compulsory voting, not the policy per se, has to be exogenous to canton‐year (or district‐referendum) specific shocks (Abadie 2005

6 The supporting information provides the exact text of the compulsory voting law (see Table 11 in the supporting information).

7 For each referendum, Table 6 in the supporting information also provides information about whether the SP endorsed it.

8 Note that some proposals were neither supported nor opposed by the SP, the FDP, or both. In these cases, parties declared a free vote. While we would have liked to also identify those federal proposals that were endorsed by the right‐wing Swiss People's Party (SVP), this is not possible because this party was not founded until 1918. Moreover, for the post‐1918 period, we find that in more than 80% of the proposals, both the FDP and the SVP held the same policy positions. We also examined the consistency of FDP and SP endorsements at the national and cantonal level. Using data from 1970, we find that these differences are negligible. For the SP, 97.4% of the endorsements by this party at the national level coincided with those by the SP in Vaud. This figure is only slightly lower (91.1%) for the FDP.

9 This choice implies that referendums in the period in which compulsory voting was temporarily suspended are no longer in the sample because there are no conflictual referendums in that period.