Comparative Public Policy Analysis: Shortcomings, Pitfalls, and Avenues for the Future

Comparative public policy is a blooming research area. It also suffers from some curious blind spots. In this paper we discuss four of these: (1) the obsession with covariance, which means that important phenomena are ignored; (2) the lack of agency, which leads to underwhelming explanatory models; (3) the unclear universe of cases, which means the inferential value of theories and the empirical results are unclear; and (4) the focus on outputs, even though most theories contain strong assumptions about the political process leading to certain outputs. Following this discussion, we then outline how a closer integration of policy process theories may be fruitful for future research.


Introduction
Many of the landmark books on public policy analysis have been comparative in nature. Esping-Andersen's study of welfare state capitalism (Esping-Andersen 1990) compared 18 Western industrialized countries to show how power resources of the left have shaped social policies and welfare state institutions; Arend Lijphart (1984Lijphart ( , 1999Lijphart ( , 2012 has used ever larger samples of countries to argue theoretically and show empirically that consensus democracies produce "kinder and gentler" (Lijphart 2012, p. 274) policies; Klingemann et al. (1994) have collected comparative evidence on how party manifestos are translated into policies in 10 Western democracies; and there are many more on the list.
What all these studies have in common is that they use cross-country comparisons to investigate whether forces of theoretical interest-power resources for Esping-Andersen, institutional features of democratic systems for Lijphart, and party ideologies measured via party manifestos for Klingemann et al.-are correlated with certain policy outcomes. Moreover, they all rely, albeit to different degrees, on quantitative data to inspect systematic covariance between countries. 1 Although the availability of time-series data has enabled researchers to use panel data and more sophisticated econometric modeling, the focus on covariance and cross-country differences is still today the backbone of this research strand in public policy analysis. Most curiously, however, the policy process-which is at the heart of many "policy theories" discussed in this special issue-is almost absent from such studies (see also John 2018).
Whether this is a strength or a weakness and to what extent possible blind spots of comparative public policy studies could be resolved by allowing the policy process to enter the stage are the key questions of this paper. To discuss these conceptual issues, we proceed in three steps. In the next section, we outline some of the key weaknesses in comparative public policy research, namely (1) the obsession with covariance, (2) the lack of agency, (3) the unclear universe of cases, and (4) the focus on outputs. After having discussed these limitations, we examine whether policy process theories as discussed in this special issue may accommodate for these blind spots. Our final section concludes with remarks on open questions and avenues for further research.

The Obsession with Covariance
Comparative public policy is a wide-ranging field focusing on very important topics such as environmental protection (e.g., Jahn 2016; Knill et al. 2010a), penal issues (Cavadino and Dignan 2006;Wenzelburger 2020), the legal rights of homosexuals (Engeli et al. 2012;Knill et al. 2015), and the welfare state (Esping-Andersen 1990; Huber and Stephens 2001;Jensen and Wenzelburger 2020). Given how broad the literature is, it is striking how constrained almost all research is in a more significant aspect: its focus on using variation between countries on some political, institutional, or economic factor to explain variation in another factor.
Examples are legion. One prominent line of work dating back several decades studies the effect of government partisanship on various outcomes (for some early, defining studies, see Hibbs 1977, Castles and McKinlay 1979, Korpi 1989, and Huber et al. 1993; for a review, see Schmidt 2010). The logic is that office-holding parties hold distinct ideological preferences over policy and that these preferences affect policy-making. The deduced expectation is that as the partisan composition of governments varies across time and between countries, public policy varies as well. The literature on government partisanship is highly advanced, and it often explores the complex conditions that constrain governments pursuing their first-order ideological preferences (e.g., Becher 2010;Jensen 2010). There is also a lively debate on how best to measure a government's partisanship. This is far from trivial, both conceptually and in terms of the empirical conclusions researchers may draw from their analyses (see the section on agency below for a more exhaustive discussion). Zohlnhöfer 2008) and is mainly concerned with explaining differences in policy outputs through correlative techniques.
Governments are nested in and influenced by the legal, political, and economic institutions of countries. In democracies, nations' constitutions obviously put very real limits on the policy-making abilities of the governments, as do the electoral rules by specifying how the governments are elected in the first place, although how exactly this happens can vary greatly from one place to another. In the United States, a system of checks and balances entails that power is shared to a much higher extent than in, say, the United Kingdom, where a single party typically dominates policy-making-a difference in governmental power that flows directly from the countries' constitutional arrangements and electoral rules. There is a large literature exploring how such institutional differences may affect public policymaking either directly or as conditional factors that moderate the direct influence of, e.g., governing parties' ideological preferences (Jensen and Mortensen 2014;Kittel and Obinger 2003;Schmidt 1996). Yet there are other, less formal institutions, too. These include a tradition for corporatist negotiations between interest groups and the government (Ebbinghaus and Weishaupt 2021), as well as a norm for public referenda rather than parliamentary legislation as an instrument of decision-making (Papadopoulos 2001;Wagschal 1997).
The focus in the literature on variation in the explanatory variables generates an intense focus on variation in policy outcomes. Indeed, a well-tested way for authors to generate an interesting "puzzle" to captivate the attention of the academic audience is to highlight how already-established variation in countries' institutional or partisan setups does not match an observed variation in policy outcome-and then move on to provide a new explanatory variable that varies in just the right way to account for the policy variation. There are good methodological reasons for the attention to variation as well, not only in the context of quantitative public policy studies, which we focus on here, but much more broadly. From historical case studies to quasi-experimental studies, variation in the explanatory variable is a vital element to establish a (maybe even causal) relationship, as a generation of political scientists has been taught by King et al. (1994) and the increasingly sophisticated literature on causal identification that has swamped the discipline.
Yet no matter the reasons, focusing on variation in the extreme way we see in the literature on comparative public policy is unwarranted. It is above all unwarranted because it is intellectually constraining. Today, all Western democracies have extensive environmental protection regimes; they all tax corporate profits; they all offer some social safety net for the poor; they all have a voting age of 18; and none punish tax evasion with death-just to mention a tiny fraction of examples that sum up to a major backdrop of similarities that is so pervasive we most of the time simply do not appreciate it. Borrowing a phrase from Baldwin (2009), ignoring these similarities has led to a "narcissism of minor differences" in comparative public policy in which variation on the margin of an explanatory variable is used to explain variation on the margin of a dependent variable (although this, of course, does not mean that variation-based studies by default are of marginal relevance).
A related trend has been the rise of what we might call institutional particularism, a phenomenon that may be even more widespread in the small-N public policy literature than in the quantitative branch. As authors jockey to explain often relatively minor differences in public policy, a forest of concepts has emerged categorizing countries into new or refined categories. This has sometimes led to awkward results, such as in the welfare state literature, in which the paradigmatic work of Esping-Andersen (1990) on welfare state regimes (itself inspired by Titmuss's work) has been relabeled and rethought dozens of times, often based on intricate arguments, but with highly decreasing analytical value. After three decades of work, the best advice to anyone interested in understanding the basic structure of welfare states in Western democracies remains to read the original book.

The Lack of Agency
Comparative policy scholars have difficulties acknowledging the role of agency when seeking to explain variance in policy outputs. This is partly due to the high level of abstraction and the number of cases that characterize most quantitative comparative policy studies: Admittedly, when analyzing policies in a large number of countries and/or over several decades, it is difficult to assess whether individual political actors and their characteristics matter for certain policy outcomes. At the same time, however, comparative public policy researchers do acknowledge that individual actors can be important for explaining policy outputs, but they also claim that they cannot account for this influence in large-N cross-case analysis (Wagschal and Wenzelburger 2012, p. 68). Given this inherent problem, public policy researchers have resorted to proxies to account for agency in different ways. The traditional solution has been to model agency on the level of collective actors, such as parties, trade unions, or nongovernmental organizations. However, in recent years, several attempts have been made to open the black box of collective actors for more finegrained analysis of individual actors. We will briefly comment on both arguments.

Theorizing Collective Agency
A prime example for the traditional way of coping with agency in macroquantitative analyses-via the introduction of collective actors-is the literature on the influence of political parties and governments. In this literature, scholars have modeled political parties as collective actors having a certain ideology to which they adhere when deciding about public policies once in government (Schmidt 1996). Hence, agency is modeled on the party level as a function of a party's ideology. To quantitatively assess the impact of party ideology at the aggregate level, different measures have been put forward. One approach is to claim that ideology can be measured via party families-a concept that was famously introduced by Von Beyme (1985). Some studies resort to a simple left-right indicator to differentiate between the ideological stance of political parties (Allan and Scruggs 2004), and others use a threefamily approach and add center or Christian Democratic parties (Huber et al. 1993), whereas the most sophisticated research employs more fine-grained measures and also accounts, for instance, for liberal parties (Wolf et al. 2014) or Greens (Neumayer 2003). 2 No matter which operationalization of party families is used, this strand of the literature concurs in modeling agency implicitly as a function of the long-standing affiliation of a party to a certain party family.
A second approach is to empirically estimate the ideological stance of a party with techniques that approximate party positions. This can be done by coding party manifestos in the tradition of Klingemann et al. (1994Klingemann et al. ( , 2006, with regular updates made available by the Manifesto Project team (Volkens et al. 2021), via expert surveys (Hooghe et al. 2010) or approaches that combine both, such as the Wordscore method (Debus 2009;Lowe 2017). In terms of theorizing agency, studies relying on party programs actually model political parties as being tied to what they say in the manifesto: Agency is doing what has been announced in the program. If expert surveys are used, the perceived position of the party in competition with others is seen as an indication of agency: Agency is modeled as parties following the ideology as perceived by experts. Finally, some authors also look at the constituencies of political parties to make inferences about their policy preferences (Häusermann 2006;Jensen 2014). Following the "electoral turn" (Beramendi et al. 2015) in political economy, this strand of research sees parties as agents of their voters. 3 Depending on the theoretical model used, preferences are tied back to the median voter position, the constituency, or the party's electorate.
These examples illustrate quite well how intricate the choices are when agency is to be analyzed quantitatively on the level of collective actors. In fact, research on political parties is very advanced and offers a lot of data to measure party positions and to model agency with the help of party ideology. For other important actors in policy-making, the modeling strategy is much more simplistic and basically assumes the preferences of collective actors. Trade unions are expected to care about wage levels and social policies, central banks about price stability, and environmental organizations about more protection of nature. While this may be true, the theoretical underpinnings are only seldomly discussed-although we do need at least a theoretical microfoundation of the preferences of collective actors if we want to make inferences about the role of agency in public policy-making. Providing such a theory-based microfoundation can be an extensive exercise, as can be seen in Scharpf's work on macroeconomic policies during the oil crises (Scharpf 1987(Scharpf , 1997.

Opening the Black Box of Collective Actors
An alternative to theorizing and modeling agency at the level of collective actors-such as parties, trade unions, or central banks-is to go to the micro level and estimate preferences of individual policy-makers that are identified as important. Qualitative studies have repeatedly shown that key actors in a certain policy area, say cabinet ministers, can strongly affect policy decisions (Wenzelburger 2020;Wenzelburger and Staff 2017;Zohlnhöfer 2009). Moreover, it is conceivable that their policy preferences are driven by a number of (sometimes competing) consid-erations: Gaining votes clearly plays an important role, but core policy beliefs also matter, and so do strategic considerations and party-specific goals an actor wants to reach (Wenzelburger and Zohlnhöfer 2020).
While it is true that quantitative studies will not be able to account for all of these factors, substantial advances have been made in bringing individual actors more fully into comparative policy research in quantitative studies. They concern two aspects: the question of whether different individual actors have similar weight in influencing policy decisions (equivalence problem), and the question of whether individual actors can have competing preferences (preference formation problem).
On the first point of equivalence, the basic question is whether individual actors that have been identified as important in policy-making are more or less influential. While this aspect has been discussed to some extent in the veto player literature with respect to the formal role of veto players (Ganghof 2003), it also matters for individual actors. How the problem of equivalence can be accounted for empirically in quantitative studies has been shown by Alexiadou (2015). In her study on welfare policies, she closely analyzes how different types of cabinet ministers-ideologues, partisans, or loyalists-are able to influence policy decisions to different degrees. Her study shows that, indeed, differences between individual political actors exist and can be included in a quantitative study: Partisans (party heavyweights and aspiring leaders) and ideologues (with strong and fixed policy preferences) are much more successful in influencing policies than loyalists, who follow the party leader.
While Alexiadou shows how one can address the problem of equivalence in quantitative studies, she still needs to make assumptions about what the preferences of political actors are (preference formation problem). To do so, she draws on the partyfamily literature to derive expectations about social welfare preferences (opposing social democrats on the one hand with liberal and conservative ministers on the other hand). However, if we want to take individual actors more seriously, we also need to cope with the fact that agency of individual policy-makers may not be driven by rather general party-family goals. To address this problem, biographical research can help to a certain extent, an idea that has mainly been followed by economists in order to explain economic policy decisions. Neumeier (2014, 2016) have, for instance, shown that the class background of political leaders matters for fiscal conservatism even when controlling for political party affiliation, with lower class status correlated to higher budget deficits. And for capital account liberalization, Chwieroth (2007) has shown that the professional background of economic policymakers matters for liberalization decisions in emerging countries. These results point out that preference formation can indeed be modeled on the level of the individual policy-maker even in quantitative studies.

The Unclear Universe of Cases
The "grand theories" of comparative policy research, such as power resources theory or institutionalist approaches, have been initially developed to explain variation between policies of Western democracies. However, the universe of the cases that the theories have been applied to has been widened significantly-as studies on postcommunist countries in Eastern Europe and Latin America illustrate (e.g. Borges 2018; Ha 2015). But are the theories of comparative policy research universally applicable, or are their explanatory claims limited to democratic systems or even only to the Western industrialized nations? Unfortunately, this important question of the universe of cases to which the theories can be applied has never really been discussed in the respective research. 4 This state of affairs is problematic because if we want to say something about whether the theoretical claims may travel to other systems, we should at least know where theories are clearly applicable (Sartori 1970). Only then can we define scope conditions and argue under which circumstances certain theorized relationships may also be expected in other contexts. To illustrate our point, we focus on two major approaches within the canon of comparative public policy theories: power resources theory/party politics and institutionalism.
For power resources theory as well as institutionalism, it seems safe to say that the DNA of these theories is strongly influenced by researchers who had political developments in Western European states and their respective consequences in mind. The key work on power resources theory- Korpi's (1983) "democratic class struggle"-has not only been influenced by neo-Marxism and the analysis of the Swedish case, but it is also clearly rooted within the theory of cleavage structures that has been devised for Western European nations (Lipset and Rokkan 1967). The cleavages identified by Lipset and Rokkan have been developed for Western European societies, and the distinct societal groups of interests, which are transported to the political systems by intermediate organizations such as trade unions or parties, are the groups created by the history of revolutions in Western Europe. Similarly, cleavage structures have been important ingredients in Lijphart's work on democratic systems, with institutional features of consensus democracies being set up in strongly "verzuiled" nations to guarantee coalition building and the protection of minorities. Hence, much speaks for restricting the very core universe of cases of these theories to the democracies in Western Europe (Austria, Belgium, Denmark, Finland, France, Germany, Ireland, Italy, the Netherlands, Norway, Sweden, Switzerland, and the United Kingdom).
However, it is true that the classics of power resources theory and institutionalism did enlarge the universe of cases and included Western industrialized nations outside Europe, such as Australia and New Zealand, the United States, and Canada: Korpi (1983) and Esping-Andersen (1990) include, for instance, 18 OECD countries, and Lijphart (1984) initially included 21 Western democracies. Thus, the universe could therefore be drawn a bit larger if we were to follow the selection criteria given by the authors themselves, namely to focus on countries that "have had a record of political democracy during the entire postwar period" (Korpi 1989).
The selection of democracies for applying power resources theory and institutionalist theories to the explanation of policies is linked to the causal mechanisms that are assumed to be at work. Clearly, theorizing about the power resources of the working class and their impact on policies requires establishing a transmission belt to bring these interests into the political game. In the literature on power resources theory, these channels are both corporate (e.g., trade unions) and political (socialist or social-democratic parties)-and at the least, the political channel needs democratic systems to work. For the influence of political institutions on policymaking, a similar point can be made. In Lijphart's (2012) work, for instance, the comparative study of institutional features that allow systems to integrate minority positions in the decision-making process makes sense only in the context of democracies. Similarly, veto-point approaches that account for the institutional barriers against policy change (Huber et al. 1993;Kaiser 1997;Schmidt 2002) have also been designed for democratic systems: They model how constitutional structures of democratic states limit the maneuvering room of governments, which is directly linked to the democratic idea of separation of powers. 5 Hence, these considerations speak in favor of including non-European democracies in the universe of cases to which power resource theory and institutionalist approaches can be applied.
At the same time, however, enlarging the universe in this way raises additional questions. First of all, if being an established democracy is the criterion of using comparative public policy theories, we have to ask ourselves whether we should not follow Lijphart's example and also include countries such as Argentina, Uruguay, and Korea to our analyses (Lijphart 2012). Most of the comparative public policy scholars refrain from doing so-mostly because they seem to feel that Latin American states such as Uruguay and Argentina are rather different from the traditional Western European democracies that have been at the core of theorizing, or from other advanced industrialized countries such as the United States and Canada. However, without giving strong theoretical reasons for exclusion, such choices quickly seem arbitrary. Consequently, the main question is whether the concepts used to form our theory would travel to a such extended universe of cases. Here, the inclusion of Australia, Canada, New Zealand, and the United States may already be criticized. The mechanisms underlying power resources theory are a nice illustration: If we take the idea of political parties as channels for power resources of societal groups (or coalitions) seriously, it is unclear whether U.S.-style political parties actually are similar to European parties in fulfilling this role, given that more fluid membership and the stronger ties of members of Congress to their local constituents weaken the "responsible party model" (Miller and Stokes 1963;Page et al. 1984). Similarly, if our institutional theory should travel to democracies in Latin America, we need to ask whether focusing on written constitutions to conceptualize institutional constraints and veto points in policy-making is actually enough, given that important collective actors "outside" the constitution have been able to influence policy decisions (e.g., the International Monetary Fund [IMF] on economic policy). Hence, if enlarging the number of cases should not lead to "conceptual stretching" (Sartori 1970), we have 5 Within the strand of institutionalist approaches, the only approach that is general enough to travel to nondemocratic contexts is Tsebelis's veto player theory (Tsebelis 2002). While it is true that this theory has been mostly applied to explain status quo bias in decision-making in democratic systems, its general ideas-of institutionally defined veto players seeing compromise by negotiation while holding distinct policy positions-can well be applied to decision-making in autocracies (Torenvlied and Klein Haarhuis 2008). to go back to theory and ask ourselves whether restricting the universe of cases does not provide us with more valid insights than applying comparative public policy theories to a universe of cases they have not been designed for.

A Focus on Outputs
One reason why much comparative public policy research is quantitative is what might best be described as a data revolution. Twenty-five years ago, the most prevalent quantitative measure of public policy was government spending-data that were collected by the IMF (e.g., government finance statistics) or the Organisation for Economic Co-operation and Development (OECD; economic outlook) and provided a reliable basis for comparison. Therefore, evidently, many of the first-wave cross-national public policy studies used different spending items of government's budgets as the dependent variable (Castles and Mckinlay 1979). This has changed dramatically as researchers have constructed large datasets with often very fine-grained information both on public policies and the theorized predictors of public policy change.
Walter Korpi and his collaborators started the Social Citizenship Indicator Programme in the 1980s, and it may be counted as an early and very successful example of a public policy dataset (Korpi and Palme 2008). Although some elements of the dataset may be better classified as policy outcomes, because they capture not only the legal entitlements of citizens but also the value of these rights compared with the incomes of other members of society, it has been immensely popular (Ferrarini et al. 2013). The Social Citizenship Indicator Programme covers 18 Western democracies all the way back to 1930 and therefore allows for an analysis of when governments introduce the right to receive old age pensions, sick pay, or unemployment benefits, as well as the conditions attached to these social rights. The landmark study of Esping-Andersen (1990) drew heavily on this data, as have several widely cited pieces by Palme 1998, 2003). In the realm of social policy, the Social Citizenship Indicator Programme has since been supplemented by the Comparative Welfare Entitlements Dataset , which provides annual data and deviates from the Social Citizenship Indicator Programme in several measurement issues (Scruggs 2013;Wenzelburger et al. 2013). Still more recently-and to overcome reliance on replacement rates that are connected to income-researchers have turned to legislation to measure policy outputs in the realm of social policy (see, e.g., the Welfare Reform Dataset [Jensen and Wenzelburger 2020]) or to even more fine-grained program-related data (see, e.g., the Comparative Unemployment Benefit Conditions & Sanctions Dataset [Knotz 2018]).
Among European researchers, Knill and his colleagues (Bauer and Knill 2014;Knill 2013;Knill et al. 2010b) arguably take first prize in the art of collecting very large public policy datasets across a wide range of policy fields-from environmental protection to moral policies to social rights-but today there is a large number of datasets, often with quite specific information. But international organizations such as the OECD have also expanded their data collection efforts, going way beyond spending. Their systematic collection of policy information from its member countries across many different policy areas has been particularly helpful in this regard and ranges, today, from employment protection rules to taxation indices to policy instruments for environmental protection-data that researchers frequently use to construct new datasets on their own. In conjunction with the similar impressive expansion of dataset measuring of government partisanship and other important independent variables (Armingeon et al. 2020), the breadth and depth of this collective effort means we today have a good grasp of the trajectories of policy developments in many different policy areas.
All qualities untold, the major problem with the data revolution and the analytical focus it implies is exactly its focus on policy outputs and outcomes. Yet almost all theories of comparative public policy emphasize the role of the policy process. The veto play theory (Tsebelis 2002), to take one example, implies a quite intricate process of bargaining between the political actors, exactly as the power resource theory does. Yet, as data are readily available, researchers are quick to dismiss more appropriate measures that may take at least some parts of the policy process into account and instead correlate what can be downloaded from the existing sources. Power resource theory is a case in point. Here, most scholars use, for instance, the data collected by Visser (2006) on trade union density, although measures of centralization or the inclusion of unions in the policy-making process may be more appropriate. Moreover, from an empirical perspective, another important issue is that there typically are many more testable observations following from a given theory than what is possible to test with the new datasets. Hence, a focus on the policy process would often be helpful in discriminating between possible explanations.

Discussion
While the comparative public policy literature has many advances, it also suffers from certain blind spots, as we have argued above. In a research field as diverse and multifaceted as this one, there are many paths open to explore in order to alleviate them. In this section, we want to highlight that one possible path is to gather insights from some of the theories and approaches that have a greater emphasis on the policy processes-and to simply make a greater effort to study the policy process as a means of evaluating theories. While this certainly is no silver bullet, greater theoretical cross-fertilization may nevertheless increase the fruitfulness of comparative public policy research in the future (see also John 2018). Much in this line of thinking depends on researchers' willingness to supplement their quantitative work with more qualitatively oriented analyses, but there are other ways to improve the state of the art. One is to be more explicit about case selection, also in the context of large-N datasets, and another is to speculate about how such datasets can begin to comprise measures of the policy process.
When it comes to the obsession with variance, which to a large extent seems to be driven by the fact that comparative public policy is interpreted as comparative cross-unit public policy, a keener awareness of processes would be helpful. While it is true that data availability has enabled public policy researchers to combine the usual cross-sectional with time-series analyses, much of the theorizing still concerns the cross-sectional rather than the over-time dimension. A promising way forward is therefore to deduce more explicit expectations about within-unit processes (or vari-ation within units, over time). Existing theories of the policy process, as discussed in this issue, can serve as starting points for such an endeavor, and several of the concepts discussed in these approaches are also open to quantification (on Multiple Streams Approach [MSA], see Engler and Herweg 2019). Most importantly, focusing on processes also enables public policy researchers to explore phenomena where there is no, or only minor, cross-unit or over-time variation. Because policy stability and/or incremental change are often caused by institutional friction (Baumgartner et al. 2006), inspecting how political institutions prevent major policy change is much easier to grasp if one deals with the policy process itself. The literature on policy drift is a nice illustration of how the study of the process can help to carve out the reasons why policies do not react to changing context (Hacker 2005). Methodologically, by investigating the policy process more closely, researchers may even be able to unearth causal process observations in qualitative process tracing (George and Bennett 2005) that may complement patterns identified in quantitative large-N analyses. Triangulating between cross-unit and within-unit analyses, of course, is something that several scholars have done successfully, but there is little doubt that even greater attention to this would be welcome.
Much the same is true when it comes to an increased focus on actors and their actions. While it is not possible to directly observe preferences, within-unit analysis of actions in context can significantly enrich our knowledge. Again, insights from policy process theories can enrich existing comparative public policy research. Because actors are key in policy process theories, major approaches such as the MSA or Advocacy Coalition Framework (ACF) teach us important lessons about how to conceptualize preferences of these actors. Advocacy Coalition Framework scholars have focused on belief systems and their components, and proponents of the MSA have carved out the skills of policy entrepreneurs, such as networking. Clearly, these insights could be used fruitfully in enhanced comparative public policy research that takes actors more seriously. Moreover, policy process theories usually move beyond assuming preferences. Instead, elaborate methodological strategies for measuring preferences on the individual level have been introduced, as the quantitative (Weible et al. 2004;Zafonte and Sabatier 2004) and qualitative (Litfin 2000) work on belief systems in ACF demonstrates. Moreover, as evidenced by the recently introduced "programmatic action framework" (Bandelow and Hornung 2020), preferences can also be rooted in shared biographies of policy elites. These insights call for a more systematic integration of actors-and advances in social network analyses may even enable quantitative researchers to include actors and coalitions more plainly in their studies.
With regard to the universe of cases, policy process theories do not seem to be very helpful for overcoming the problems of the mostly quantitative comparative public policy research-at least at first sight. Because studies applying policy process frameworks often zero in on one certain policy process, such as a governmental decision, a reform, or a certain policy in a single country, even more serious "travelling problems" seem to arise if we want to generalize to other cases. However, there are also advantages in gaining "internal validity" in single-case studies, as the causal processes can be identified more clearly and the specificities of a certain causal pathway can be carved out (Pepinsky 2019). A focus on policy processes within cases enables researchers to study nonvariance as well as variance within cases Causal drivers for nonvariance (that is, policy stability) have to be considered explicitly, e.g., via the study of drift Causality claims are based not on the occurrence of covariance but on causal process observations Actors Actors are key in policy process theories (policy entrepreneurs, advocacy coalitions, etc.), and these theories conceptualize their preferences Methodologically, preferences of actors are not assumed but are investigated (usually qualitatively) Universe of cases At first sight, the universe of cases is even more constrained, but, at the same time, the selection criteria and scope conditions are often much more clearly pointed out Generalizing from causal process observations may be possible if scope conditions are clearly identified Focus on outputs Policy process theories have a greater focus on processes instead of outputs both theoretically and when establishing (causal) relationships empirically Clearly, well-executed single-case studies investigating the policy process need to be clear about the case selection criteria and need to discuss the scope conditions when making generalizing claims. Whether theoretical concepts travel to other contexts (see, for instance, the articles on MSA and programmatic action framework in this special issue) is a question that cannot be easily answered. However, at least from our impression, researchers presenting single-case studies often do discuss these questions much more explicitly than comparatists conducting large-N analyses on convenient samples selected based on available data. Hence, while it is true that the universe of cases is certainly more diverse in comparative studies of public policies than in the usual single-case study applying policy process theories, the methodological reasoning underlying case selection is often more clearly spelled out in single-case studies. At least, the lesson that case selection should always be meaningfully discussed, even in large-N comparative studies, can be learned from policy process theories.
On the last weakness of existing comparative public policy research (see Table 1), the focus on outputs, our discussion above has already pointed out the disconnect between theories-which are often about processes-and the analytical focus on policy outputs typically used in such studies. It is crystal clear that more process-related evidence is a desideratum for such research, although the concrete way forward is not always easy for quantitative researchers. While some process-related indicators may be developed, and the availability of time-series data may alleviate some of the problems, much of this work on causality will probably be qualitative in nature. Hence, this weakness can probably more plainly be tackled when both theoretical perspectives and their most widespread methodological approaches (quantitative for comparative public policy research [CPR] and qualitative for policy process research [PPR]) are combined. It is to this point that our final section will turn.

Combining Process and Comparison? Some Thoughts on Future Policy Research
Theories of comparative public policy research have generated important insights into the patterns of public policy outcomes and outputs in, mostly, Western industrialized countries. Theoretical approaches such as power resources theory and institutionalism have developed into major lenses and contributed to theory development in policy research and beyond. Nevertheless, our discussion of the state of affairs in this research program has shown that several weaknesses exist in comparative public policy research, which are partly due to methodological choices and can also be explained by the level of abstraction that usually characterizes these studies.
In the last section, we discussed how a closer look at theories of the policy process may help to overcome some of the weaknesses of comparative public policy research. With their focus on the process, these approaches contribute to the understanding of why certain policy decisions have been made by looking more closely at individual actors, their choices, and the individual elements that have produced these choices. In addition, because these studies often look at single cases or a small number of cases, they tend to reflect more deeply on the scope conditions and selection criteria of their cases. Hence, our analysis shows that some of the weaknesses in existing comparative public policy research are not carved in stone but can indeed be remedied by carefully integrating policy process theories into the theoretical arguments and the empirical research design of comparative policy research.
Pursuing this idea of combining comparative public policy research from the covariance-oriented tradition with a more fine-grained study of the policy process raises the question of how this could be executed in empirical practice. In our view, combining process and large-N comparison entails at least two key aspects that need to be addressed. First, on the theoretical level, researchers have to establish a theoretical nexus between the causality-as-covariance approach of comparative public policy studies and the causality-as-process view of process-oriented work. This means thinking more closely about how general approaches such as power resources theory may be applied in a process-oriented framework, such as the MSA or ACF. Recent examples show that this is indeed possible: In his analysis of partisan influence on British law and order policies during the New Labour governments, Staff (2018) links the rather general party politics argument from the comparative public policy literature to the MSA via the concept of the policy entrepreneur and the "policy-seeking party elites mechanism" (Staff 2018, p. 31). Similarly, Sager and Thomann (2017) also integrate party politics in the MSA in their study of Swiss asylum policies. They argue that the strengths of left-wing and right-wing parties can be conceptually integrated in the politics stream of the MSA and show empirically that the presence of different parties can help to explain the restrictiveness of asylum policies in Switzerland. Finally, Herweg et al. (2015) amend the MSA to more fully account for the role of political institutions. However, other policy process theories can also be combined theoretically with party politics: Walgrave and Varone (2008) call for the integration of political parties in punctuated equilibrium theory, while Hornung and Bandelow (2021) discuss how partisanship of individual actors can be used in the ACF. While these examples show that first steps forward have already been taken in the literature and seem to provide interesting insights, it seems clear that more theorizing about how elements of policy process theories can be combined with more general accounts of cross-national comparisons is warranted in order to address the weaknesses of current comparative public policy research. Staff's work on the political economy of private security, in which he blends several "usual suspects" of comparative policy research-such as socioeconomic changes, political parties, and institutions-into the logic of MSA, may serve as a starting point for such endeavors (Staff 2020).
The second aspect concerns the combination of qualitative and quantitative methods. Indeed, a close study of the policy process to unearth causal relationships has mostly been done by qualitative methods such as process tracing, whereas comparative public policy research mostly relies on quantitative techniques to find correlations between the relevant dependent and independent variables. To combine these strands, therefore, a methodologically sound way to connect covariance-oriented and case-oriented methodological approaches needs to be found. Fortunately, the literature on how to combine quantitative with qualitative methods has been growing over the years and includes several proposed ways to mix these approaches (Beach and Pedersen 2016;Creswell and Plano Clark 2018;Lieberman 2005). Such mixed-method designs therefore are a promising avenue for combining the strength of quantitative studies to identify correlational patterns in the data of many nations with the strength of qualitative studies to trace the causal processes that lead to a certain outcome.
In a sense, some of the older literature comparing public policies has even been closer to what we see as a promising route to mutual stimulation than some more recent work, even though these studies were less advanced methodologically and used mixed methods in a much more implicit way. Nevertheless, research by firstclass comparativists such as Schmidt (1980) or Huber and Stephens (2001), which is mainly based on quantitative methods comparing nations, is often full of implicit qualitative evidence. While this evidence is not integrated in an advanced mixedmethods design, the discussion of country specificities and the illustrations of the correlative patterns found in the quantitative data by means of examples show how deeply the researchers actually knew their cases and give a high degree of face validity to their quantitative results. Hence, although these studies could not use the most advanced techniques of causal identification, the presentation of correlative patterns and the depth of descriptive and illustrative evidence included in the discussion of the cases did indeed add up to at least a very plausible argument about causal relationships. While the rapid development of causal identification techniques may indeed help scholars from political psychology or economics who use individuallevel data, the way forward in comparative policy research could be quite different. Based on the arguments put forward in this essay, we would hold that combining comparative public policy theories with policy process theories and mixing quantitative pattern identification based on correlations with deep case study knowledge may be a much more promising avenue to deliver robust insights on the reasons why public policies differ between countries and why they change over time.
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