Drivers of parliamentary opposition in European Union politics: institutional factors or party characteristics?

ABSTRACT A vital political opposition is one of the cornerstones of democracy, yet we know surprisingly little about the conditions that shape it. In this paper, we offer a comprehensive assessment of the drivers of parliamentary opposition in European Union (EU) politics in five countries: Denmark; Germany; Ireland; Sweden; and the United Kingdom. Based on an extensive hand-coded data set of 7,520 statements made by members of parliament (MPs) during both plenary sessions and deliberations during European Affairs Committee (EAC) meetings, we examine how institutions and party characteristics shape two types of oppositional behaviour: the expression of critique and the presentation of alternatives. We find that both factors are important for understanding to what extent, and how, opposition is voiced in national parliaments. Oversight institutions’ strength and a party’s degree of Euroscepticism jointly function as significant determinants of the likelihood that MPs will express opposition in the form of critique. However, when it comes to the likelihood of offering alternatives, oversight institutions’ strength fails to explain variations in the share of alternatives, while degree of Euroscepticism remains a significant predictor.


Introduction
The right to organize opposition is one of the 'milestones of democracy' (Dahl, 1966, p. xi;Mair, 2007).Opposition provides a critical voice that forces the government to defend its policies, vesting voters with meaningful alternatives and real choices.Therefore, it is unimaginable that democracy could be sustained in the absence of opposition.Previous research has identified two main drivers of opposition in European Union (EU) politics: political party dynamics (e.g., de Vries & Hobolt, 2020;Hooghe & Marks, 2009) and institutional opportunity structures (e.g., Auel et al., 2015aAuel et al., , 2015b;;Garritzmann, 2017;Winzen, 2012Winzen, , 2021)).Nevertheless, the relationship between different institutional setups and party characteristics, and their association with oppositional behaviour have never been put to the test in a single study.This paper aims to examine how differences in the strength of institutions involved in parliamentary EU scrutiny and parties' positioning in EU politics affect oppositional behaviour.We ask: How do institutional factors and party characteristics shape parliamentary opposition in EU politics?
According to influential scholars, the political dynamic that we have been witnessing in Europe over the past few decades, i.e., increasing support for Eurosceptic parties, is one primarily driven by party behaviour (Hix, 2013;Mair, 2007Mair, , 2013)).For a long time, decision-making within the European Union (EU)from the EU level down to the domestic spherewas depoliticized as mainstream parties refrained from getting involved in conflict over EU affairs.Voters were deprived of alternatives to policies that the political mainstream proposed, creating an alleged 'opposition deficit' in EU politics (Karlsson & Persson, 2018;Rauh & de Wilde, 2018).As a consequence, political actors that perceived a lack of real opportunities to organize opposition increasingly ended up opposing the political system itself.This situation functioned as a breeding ground for Euroscepticism, anti-systemic sentiments and right-wing populism.By challenging the political mainstream, Eurosceptic parties raised the salience of European integration in domestic politics, succeeded in national elections and referendums, and acted as the main driving forces of opposition in EU politics (Brack & Startin, 2015; de Vries & Hobolt, 2012, 2020;Hooghe & Marks, 2009;Hutter & Grande, 2014).
However, other important strands of research have pointed to institutional factors as key drivers of oppositional behaviour more generally.For instance, Garritzmann (2017) suggested that differences in institutional opportunity structures across countries are what mainly drive cross-national variation in oppositional behaviour.Similarly, and with a specific emphasis on EU politics, Auel et al. (2015aAuel et al. ( , 2015b) ) found that the strength of the institutions involved in parliamentary scrutiny of governments' EU policies are particularly important drivers of parliamentary activity in EU affairs.This literature on legislatures acknowledges the importance of the institutional context for understanding parliamentary control in EU politics (e.g., Karlas, 2011;Winzen, 2012Winzen, , 2021)).However, this insight has not been used to examine actual oppositional behaviour, which this article aims to do.
We depart from a theoretical distinction between two crucially important types of opposition (Garritzmann, 2017, p. 2): the expression of critique and the presentation of alternatives.By expressing critique, political actors can exercise control over the government by 'supervising and monitoring policy-making, as well as influencing, shaping, sanctioning, and limiting it' (Garritzmann, 2017, p. 7).However, by presenting alternatives, political actors seek 'to present different policies, different methods to achieve the same goals, or alternative political personnel' (Garritzmann, 2017, p. 7).While the former type of opposition is important for controlling the government and magnifying voices in EU politics, the latter type concerns introducing choices and presenting voters with alternatives to the sitting government.
By examining these two types of oppositional behaviour based on a data set of 7,520 statements by parliamentarians in five countries -Denmark, Germany, Ireland, Sweden and the United Kingdom (EU member states at the time of our investigation)our study advances the understanding of the forces driving parliamentary opposition.We selected our countries strategically to obtain variation in institutional constraints, as well as party characteristics.Thus, we are in a position to compare to what extent variations in institutional opportunity structures and party dynamics affect actual behaviour.Our sample includes national parliaments with varying degrees of institutional strength in EU politics (Auel et al., 2015a;Winzen, 2012Winzen, , 2021)), as well as parliaments in which Eurosceptic parties have been more and less influential.We are therefore able to inquire whether opposition in EU politics is stronger in member states where Eurosceptic parties have been successful, or even part of the mainstream, than in member states where they have been late-comers or less successfuland how institutional factors help shape such patterns of opposition.
The article proceeds as follows.First, we briefly review the state of the art in research on oppositional behaviour in EU politics.Next, we present our conceptual framework and develop the theoretical expectations that guide our examination.We then lay out our data collection procedures and methodology, followed by our assessment of how institutional setups and party characteristics affect oppositional behaviour.We end the paper with our conclusions.

Previous research on oppositional behaviour in EU politics
A key development in European politics over the past few decades has been the growth of parties that challenge the political mainstream in EU affairs.Eurosceptic parties have used their resistance to European integration to gain electoral success in national elections and referendums ( de Vries & Hobolt, 2012, 2020;Hobolt & de Vries, 2015).The representation of Eurosceptic parties in national parliaments has fuelled the politicization of European integration and led to party position shifts among mainstream parties (Filip, 2021;Meijers, 2017;Persson et al., 2022).The growing importance of Eurosceptic parties that challenge the political mainstream underscores the significance of party dynamics for understanding various aspects of EU politics.Thus, prior research has examined a wide range of issues in connection to Eurosceptic parties, and we now know a lot about their party positions (Hooghe, 2007;Taggart & Szczerbiak, 2013), electoral strategies ( de Vries & Hobolt, 2012;Hobolt & de Vries, 2015;Hoeglinger, 2016), impact on EU discourses and practices (Brack & Startin, 2015;de Wilde & Trenz, 2012;Louwerse et al., 2021;Rauh & de Wilde, 2018), voting behaviour (Louwerse et al., 2017;Tuttnauer, 2018) and the role they play in national parliaments' scrutiny of EU affairs (Hoerner, 2017;Senninger, 2017).However, despite growing interest in the role that Eurosceptic parties play in EU politics, much remains to be learned when it comes to the importance of party dynamics for understanding oppositional behaviour in EU politics.Some recent studies have focused on the role that Eurosceptic parties play when it comes to domestic parliamentary opposition in EU affairs (Hoerner, 2017;Karlsson & Persson, 2018, 2022;Persson et al., 2019;Senninger, 2017;Tuttnauer, 2018).However, we lack research that systematically examines the linkage between party characteristics and oppositional behaviour in different institutional contexts.
Previous institutional research into EU politics includes an important strand that focuses on the design of oversight institutions, as well as the development of parliamentary EU activity and scrutiny at the domestic level (e.g., Auel et al., 2015aAuel et al., , 2015b;;Bergman, 1997;Helms, 2008;Karlas, 2011;Raunio, 2005;Winzen, 2012Winzen, , 2021)).This research has mainly focused on the presence of opportunity structures (above all oversight mechanisms) that may be instrumental for national parliamentarians as they seek to voice political opposition in EU affairs.It has delivered crucial insights regarding how different forms of parliamentary activity in EU affairs differ between member states (e.g., Auel et al., 2015b;Holzhacker, 2002Holzhacker, , 2005)), but it has not confronted oppositional behaviour head on.
However, some studies have focused on how institutional factors impact political opposition.For example, Garritzmann (2017) compared the institutional prerequisites for political opposition in 21 democracies and made an important contribution to our understanding of opposition patterns by emphasizing institutional opportunity structures' importance, as well as providing comparative data on institutional opportunity structures in 21 democracies.However, considering that it takes a strictly institutional perspective, Garritzmann's contribution did not shed any light on the nexus of party dynamics and institutional factors that we investigate in this paper and find to be key factors in understanding oppositional behaviour in EU affairs.Similarly, a study by Mårtensson et al. (2021) investigated how institutional factors shape opposition towards the EU's scheme for free movement across 12 countries, but focused on citizen attitudes, rather than those of parties and parliaments.
Thus, in summarizing existing research in the field, we found studies with an institutional perspective that left party dynamics out of the picture, as well as studies that zeroed in on the importance of party characteristics, without systematically controlling for institutional factors' impact (for notable exceptions, see, e.g., Benz, 2004;Helms, 2008;Holzhacker, 2002Holzhacker, , 2005)).However, two prior studies deserve extra attention, as they came close to realizing the present article's goals.In a comparative study of 16 EU member states, Tuttnauer (2018) examined which party characteristics make opposition parties more likely to 'either confront the government on plenary votes or cooperate with it' (p.279).The results indicate that party characteristics as well as systemic featurese.g., the strength of parliamentary committee systems and the openness of competition structuresexplain variations in opposition parties' behaviour; i.e., both party dynamics and institutional factors are determinants of oppositional behaviour.Hoerner (2017) investigated to what extent Eurosceptic parties use resolutions in national parliaments to express opposition.He found that Eurosceptic parties issue more resolutions than mainstream parties and that their content is very critical, whereas mainstream parties' resolutions usually support the government.Thus, Hoerner found that the strength of the formal scrutiny powers enjoyed by the five parliaments included in the study exerted 'a positive effect on the number of resolutions being issued ' (p. 316).The study clearly demonstrated that party characteristics are crucial to understanding variations in oppositional behaviour, but the results also confirmed that institutional factors matter.
While we draw inspiration from these studies, our investigation differs from them in three important ways that will position us to shed new light on oppositional behaviour.First, our study provides a more comprehensive picture of oppositional behaviour by including data from both main arenas in parliament where parties debate EU politics, the plenary and the EAC, whereas Hoerner (2017) and Tuttnauer (2018) leave the EAC out of the picture by focusing on the issuing of resolutions and plenary voting.To the best of our knowledge, there is only one previous study on political opposition which includes behaviour in the plenary as well as in the committee.This investigation (Karlsson et al., 2022), however, is content with describing differences in MP oppositional behaviour between the two arenas, rather than seeking to uncover the drivers of parliamentary opposition in EU affairs.
Second, this investigation focuses exclusively on oppositional behaviour, whereas the study by Hoerner (2017) is more broadly focused on parliamentary activity associated with government control.Expressing opposition may be a way to seek to exercise control over the government, but not all opposition is voiced with this goal in mind.Opposition is also a way to present voters with alternatives to the government's policies.Tuttnauer (2018), on the other hand, puts the behaviour of opposition parties, rather than oppositional behaviour centre stage.This distinction is crucial to uphold because neither theoretically nor empirically can we equate behaviour by opposition parties with oppositional behaviour.MPs representing opposition parties will sometimes support the government, just like MPs from governing parties occasionally will engage in oppositional behaviour.
Third and most importantly, this study uses an operationalization of oppositional behaviour designed to ensure high content validity.As pointed out in the introduction, classic scholarly works on opposition (Dahl, 1966;Mair, 2007Mair, , 2013) ) have made a crucial distinction between opposition in the form of expressing critique directed at the government and opposition in the form of presenting alternatives to the government's position.The studies by Tuttnauer and Hoerner both lack this crucial distinction, which we are able to capture through our qualitative coding of content in MP statements.To be fair, there is previous research on political opposition that does take both these dimensions of oppositional behaviour into account (e.g., Karlsson & Persson, 2022;Persson et al., 2019), but these studies do not examine how institutional factors and party characteristics work together to shape parliamentary opposition.
To sum up, when examining the state of the art we find important work on oppositional behaviour that consider both party characteristics and institutional factors.The present study seeks to move beyond these studies by offering a comprehensive and focused study with high validity.

Conceptual framework and theoretical expectations
As with many key concepts in political science different definitions of opposition exist in the literature (Norton, 2008).An exhaustive conceptual discussion lies well beyond this article's scope, but this should not be made more complicated than it needs to be.First and foremost, we are concerned exclusively with parliamentary oppositionmore specifically oppositional behaviour that takes place either in plenary or committee work.Second, we see opposition as a type of behaviour that signals conflict in words or deeds.Thus, it is the actor's behaviour, rather than characteristics, that is the defining element of opposition.Finally, we focus exclusively on disagreement directed at the government, rather than other types of conflict that may occur between MPs.Thus, the theoretical understanding of opposition from which our investigation proceeds comes close to Robert Dahl's minimal definition, which states that opposition occurs when an actor 'B is opposed to the conduct of government A' (Dahl, 1966, p. xviii).Thus, in line with Dahl, we define opposition as an expression of disagreement with the government.This definition does not reserve the concept of opposition for disagreement with the government over policy, i.e., what has been labeled 'classical' opposition (cf.Dahl, 1966;Kircheimer, 1957).Aside from disagreement over policy, two other modes of opposition exist.Kircheimer (1957) distinguished between disagreement directed at the whole system of governance and disagreement directed at conduct in politics, and how the government acts.In this article, we do not differentiate between these modes of opposition, but view all opposition to the government as significant.
As we set out to chart oppositional behaviour in EU politics, we first determine whether statements made by MPs during plenary debates or EAC committee deliberations contain disagreement with or support for the government.If a statement expresses disagreement with the government, we then ascertain whether the MP is content with simply criticizing the government or goes on to also presenting alternatives.If an actor disagrees with the government, presenting critique is the most basic way to make opposition publicly known.Expressing critique typically serves two purposes: It can either function as a means for controlling the government (Garritzmann, 2017, p. 2), or as a way for opposition parties to distance themselves from the government and make themselves more visible to voters (Norton, 2008, p. 238).MPs are often content with voicing opposition in the form of critique, but we also find regular occurrences of statement where MPs start out by criticizing the government and then move on to presenting alternatives.Opposition in the form of presenting alternatives is important because it provides voters with choices that ultimately are a perquisite for meaningful elections (Mair, 2007) and an effective democratic process.(For further discussion of the conceptual distinction between opposition as expressing critique and presenting alternatives, see the Online Appendix B).
Unlike previous research that has assumed behaviour goes hand in hand with institutional opportunity structures or follows automatically from them (cf.Auel et al., 2015a, p. 287), we put this assumption to the test by examining to what extent variation in oppositional behaviour is associated with institutional opportunity structures and party characteristics.Following previous research by Kaiser (2008) and Garritzmann (2017), the present study draws a basic distinction between institutional opportunity structures (Kaiser, 2008, pp. 25-28), i.e., the institutional setup and existing conditions for opposition to materialize on the one hand, and actual oppositional behaviour on the other.
So, what theoretical expectations can be formulated in light of previous research?As stated above, strong oversight institutions appear to be a prerequisite for national parliaments to be able to control their governments in EU politics.Scholars have found evidence that strong oversight institutions are conducive to EU debates (Auel et al., 2016;Rauh & de Wilde, 2018).Auel et al. (2015a) also found that strong institutions facilitate more activity in EU affairs, e.g., raising the number of resolutions and increasing the duration of debates and the time spent on EAC meetings.While the increased levels of activity do at least indirectly provide evidence of more active opposition parties we still have limited knowledge about oversight institutions' effects on MPs' oppositional behaviour.To see how oversight institutions may affect oppositional behaviour, we first must consider what purpose such institutions serve.Winzen (2021, p. 2) distinguishes between two types of oversight institutions: information-related and constraining institutions.Informationrelated institutions comprise the scope of information rights, the strength of mechanisms for involving sectoral committees and whether governments are required to explain their EU positions through explanatory memoranda.These institutions ultimately aim to keep the parliament informed about the government's conduct in EU politics.Constraining institutions, on the other hand, comprise scrutiny reserves and mandating rights that provide the parliament with instruments designed to force the government to consider its preferences when negotiating in Brussels.
Thus, strong oversight institutions afford MPs with the means to exert influence over the government's actions in EU politics, thereby partly fulfilling the same purpose as expressing opposition in the form of critique, i.e., controlling the government.At least two mechanisms may work to reduce MPs' incentives to express opposition as critique when strong oversight institutions are in place.First, the presence of information-related oversight institutions may reduce the risk of the parties in parliament feeling left in the dark by the government, not receiving relevant information at the right time.This means they will have less reason to criticize the government down the line.Second, the presence of constraining oversight institutions may have the effect of the government being less likely to deviate from the parliament's preferences, anticipating that the latter could use its institutional prerogatives to exercise control and scrutinyor even stop the government in its tracks.In light of this, we contend that strong oversight institutions will reduce MPs' incentives to express opposition in the form of critique at both the plenary and committee levels, as they already have instruments at their disposal to control the government.
However, the expression of opposition in the form of alternatives follows a different logic.Whereas opposition in the form of expressing critique primarily is a way to control the government, opposition in the form of presenting alternatives is, first and foremost, a way to communicate with voters.The incentives for expressing opposition in the form of alternatives should be understood against the current backdrop: Parties compete for votes in an 'electoral market' (cf.de Vries & Hobolt, 2020).MPs from parties who disagree with the government sharpen their electoral profiles and seek to attract new voters by presenting alternatives to policies that the government promotes (Auel et al., 2015a , p. 291;Norton, 2008, p. 238).The fact that opposition in the form of presenting alternatives primarily is about communicating with voters, rather than controlling the government, means that it remains a necessity regardless of the opportunities to exercise control through strong oversight institutions.Moreover, strong oversight institutions actually provide MPs with additional opportunities to express opposition in the form of presenting alternatives, e.g., by issuing resolutions.Consequently, we expect that MPs in parliaments with strong oversight institutions will express more opposition in the form of presenting alternatives than MPs in parliaments with weak oversight institutions.Thus, we propose our first set of hypotheses: H1a: Stronger oversight institutions decrease the likelihood of MPs expressing opposition as critique.
H1b: Stronger oversight institutions increase the likelihood of MPs expressing opposition as alternatives.
Let us now explore what theoretical expectations we may tease out by deploying a party perspective on oppositional behaviour.Intuitively, one would expect Eurosceptic parties to express more opposition in EU politics than mainstream Europhile parties.After all, they are labeled Eurosceptic because they are fundamentally critical of the European integration project.While this does not need to be a truism (with a Eurosceptic party in government, as in the UK during the period studied, Europhile parties may be equally inclined to push back on the government's negotiating positions at the EU level as Eurosceptic parties would be in the reverse situation), previous research indicates that it holds in most cases (Hoerner, 2017;Karlsson & Persson, 2022).
Moreover, following Karlsson and Persson (2022), we argue that Eurosceptic parties focus more on delivering critique than presenting alternatives when they express opposition in EU politics.In a study on parliamentary resolutions, Hoerner likewise found that resolutions initiated by Eurosceptic parties were highly critical, but 'rather short and contain little detail ' (2017, p. 320).Similarly, Senninger demonstrated that the opposition that Eurosceptic parties express often is directed at 'general issues such as EU treaties and institutions ' (2017, p. 286).Thus, previous studies indicate that Eurosceptic parties are prone to expressing opposition in the form of critique directed at general issues.However, mainstream parties are contenders for forming the next government, and as such, they have stronger incentives to compete for votes by presenting alternatives to the policy positions that the sitting government has communicated.As they generally are supporters of the EU project (i.e., Europhile), we expect mainstream parties to compete on the EU dimension by offering a distinct electoral profile to voters instead of relying on critique.Accordingly, we hypothesize that Europhile parties' and Eurosceptic parties' incentives are different, such that: H2a: MPs from more Eurosceptic parties are more likely to express opposition as critique.
H2b: MPs from more Europhile parties are more likely to express opposition as alternatives.
As argued above, MPs in parliaments with strong oversight institutions generally are expected to have less reason to express opposition in the form of critique, as they employ other means to control the government.However, maintaining party competition over EU issues is of key importance to Eurosceptic parties, which strive to reap electoral benefits by confronting mainstream Europhile parties in EU politics ( de Vries & Hobolt, 2012;Hobolt & de Vries, 2015).Accordingly, we expect Eurosceptic parties to continue to articulate high levels of opposition by both presenting alternatives and expressing critique, regardless of whether oversight institutions are strong or weak.
However, mainstream Europhile parties are likely to be content with exercising control over the government through strong oversight institutions whenever possible, making them less prone to expressing opposition as critique in contexts in which oversight institutions are strong.Their key priority as contenders for forming the next government is to present alternatives to the policies for which the sitting government advocates.In the presence of strong oversight institutions, we therefore expect mainstream Europhile parties to focus on expressing opposition in the form of alternatives instead of critique in order to offer the electorate substantive reasons to vote for them.Thus: H3a: The negative effect of stronger oversight institutions on the likelihood of MPs expressing opposition as critique is more pronounced for Europhile parties than for Eurosceptic parties.
H3b: The positive effect of stronger oversight institutions on the likelihood of MPs to express opposition as alternatives is more pronounced for Eurosceptic parties than for Europhile parties.
Having presented the analytical framework and the theoretical expectations, we now present our research design and methods.

Case selection, data and methods
The present study uses a qualitatively coded data set of statements made by MPs in plenary and EAC deliberations in Denmark, Germany, Ireland, Sweden and the UK.These countries were selected based on a mix of theoretical and methodological concerns.To obtain results that are generalizable beyond the selected countries' scope, we chose cases strategically using factors that may influence variation in oppositional behaviour.If we examine member state characteristics that often are used in comparative EU studies, it is far from obvious why factors such as country size, length of membership or geographical placement should matter in the context of political opposition.Instead, we focused on three factors that we believe are more likely to impact the demand for and supply of opposition in EU politics.
First, we know that substantial variation in public support for the EU exists across the member states, i.e., a greater demand, so to speak, exists for opposition in countries where a large proportion of the public is sceptical of European integration.Second, we may expect the supply of opposition in EU politics to co-vary with the strength of Eurosceptic parties in the national political system.Finally, parliaments differ when it comes to the formal powers they are afforded to deal with EU matters, and we expect to find more opposition wherever national parliaments' formal oversight mechanisms are strong.
In light of these potential drivers of opposition in EU politics, we included member states in which public support for the EU historically has been strong (e.g., Germany and Ireland), as well as member states where the public historically has been more sceptical of the EU (e.g., Sweden and the UK).In our five countries, we also found variation in the share of seats that Eurosceptic parties hold in parliament.In Denmark, Sweden and particularly the UK, Eurosceptic parties have held relatively large shares of seats in parliament, whereas they were less successful in Ireland and Germany during the period surveyed.Finally, based on previous rankings of national parliaments in terms of their institutional strength in EU politics (cf.Winzen, 2012Winzen, , 2021; see also Auel et al., 2015b;Garritzmann, 2017), our sample includes two highly ranked parliaments (Denmark and Germany), two mid-ranked parliaments (Sweden and the UK) and one low-ranked parliament (Ireland).
In order to present a comprehensive picture of oppositional behaviour, the present study builds on data from the two main arenas where EU affairs are being discussed in parliament: the committee and the plenary.To examine political opposition in terms of actual behaviour requires access to highquality data that allow us to analyse political statements' content in great detail.This is usually not a problem when it comes to plenary debates because most parliaments provide access to stenographic protocols.While it is usually quite easy to access minutes from plenary sessions, the same cannot be said about committee deliberations.When it comes to committee meetings, we usually must make do with short summary protocols that provide only limited information about the deliberations' content.However, EACs are an exception to this rule because these committeesin some, but far from all member statesprovide access to extensive minutes that allow for a detailed examination of deliberations.Ideally, we would have included deliberations in sectoral committees as well, as these have become more involved in EU affairs in the post-Lisbon era (Gattermann et al., 2016).This, however, has not been possible as these committees do not release detailed information about their deliberations.Notwithstanding the trend towards increased involvement by sectoral committees, there can be no denying that the EAC still is the most important forum for interaction between the government and the political parties on EU affairs.The key role played by the EAC is confirmed by our data, which shows that EAC deliberations cover no less than twenty policy fields where committee members discuss everything from technical aspects of EU fishery policies to how to deal with the migration crisis and the adoption of new treaties (see the Online Appendix A, Table A4 and A5).
To obtain estimates of oppositional behaviour that are representative of all the statements on EU affairs in the plenary and EAC contexts, we rely on random sampling (for more information on the sampling procedure, see the Online Appendix B).The fact that EAC meetings deal exclusively with EU affairs, means that all statements made during these sessions should be included in the sampling frame.Identifying EU statements from plenary sessions proved to be more challenging.Including only statements from debates focused exclusively on EU affairs would have resulted in us leaving out a large number of relevant statements since deliberations on EU affairs often appear during sessions categorized as 'resolution debates', 'parliamentary questions', etc.In order to identify the sampling frame for plenary statements we had to conduct a manual search for statements concerning EU affairs among all categories of plenary debates in the five legislatures.
Altogether, our data set contains 7,520 hand-coded statements from the 2009-2016 period.A little more than half (3,960) of all statements come from plenary sessions, with the remainder (3,560) coming from EAC meetings.The time frame was selected to ensure maximum comparability between countries and across arenas.Thus, we selected legislative periods as close as possible to each other in our five countries (for an overview of examined legislative periods and sample sizes, see the Online Appendix, Table A1 and  B1).
The units of analysis in our study are statements made by individual MPs representing 40 national parties (see the Online Appendix, Table A2).The statements were derived from MPs' oral contributions in two arenas: plenary sessions and EAC meetings.In most cases, each contribution contains only one statement, but in some cases, an MP may touch on two (or more) separate issues in a contribution.In these instances, the contribution was divided into separate statements before it was coded.Based on distinctions between alternatives, critique and support, we constructed two dependent variables: First, 'critique' measures whether a statement contains opposition (1 = Yes, 0 = No) in the form of a critique.Second, 'alternatives' measures whether a statement contains opposition in the form of alternatives (1 = Yes, 0 = No).For more information on the coding process, see the Online Appendix B.
To test our expectations, we run multivariate logistic regressions, as both of our dependent variables are binary.Thus, we report odds ratios in the regression table.To control for possible differences between debates on different types of policies, we run all models with policy-area fixed effects.Altogether, 20 policy areas were identified and defined based on the various configurations of the Council of the EU, followed by further division into traditional policy areas.As the data is clustered within the five countries, we utilize country-clustered standard errors.Due to the lack of within-country variation in the index of oversight institutions, we do not include country fixed effects when examining the effect of oversight institutions on the probability of MPs expressing critique and offering alternatives (Models 1 and 2 in Table 1).However, we do introduce country fixed effects when we evaluate the interaction effect of party characteristics and institutional factors on oppositional behaviour (Models 3 and 4 in Table 1).
To assess Eurosceptic parties' influence on oppositional behaviour in parliaments, we employ the independent variable 'EU position' from the Chapel Hill Expert Survey (CHES) (Jolly et al., 2022).We use linear interpolation to fill data gaps in this variable.'EU position' measures the overall orientation of a party's leadership towards European integration in a given year on a scale from 1 (strongly opposed) to 7 (strongly in favour).In other words, low values on this variable indicate that a party is Eurosceptic, whereas high values indicate that it is Europhile.The influence of institutional factors on oppositional behaviour in parliament is examined using the independent variable 'oversight institutions', based on Winzen's measure of national parliaments' institutional strength in EU affairs (Winzen, 2012(Winzen, , 2021)).The scores run between 0 (weak) and 1 (strong), with Sweden registering 0.54, Germany 0.63, Denmark 0.67, the UK 0.58 and Ireland 0.42.
To control for additional party factors, we separate government parties from opposition parties by including the dummy variable 'government party' (1 = Yes, 0 = No).While we naturally expect more opposition from parties that are not in government, previous research (Saalfeld, 2005) has demonstrated that representatives of government parties do express opposition during parliamentary deliberations.We control for parties' parliamentary 'seat share' based on the ParlGov data set (Döring & Manow, 2019), using a continuous variable measuring the share of seats in parliament that a party holds in a given year.Furthermore, we rely on CHES data (Jolly et al., 2022) to include the variable 'left-right', which reports a party's overall ideological stance in a given year on a scale from 0 (extreme left) to 10 (extreme right) again using linear interpolation to fill in data gaps.We also include an interaction variable combining 'EU position' with 'oversight institutions' ('oversight institutions * EU position'), which we use to evaluate Hypotheses 3a and 3b.Finally, two additional institutional factors are incorporated as control variables: We include the dummy variable 'arena', which represents the parliamentary arena in which a statement was presented (1 = committee, 0 = plenary).Since prior research shows that the electoral cycle may impact oppositional behaviour in parliament (e.g., Schwalbach, 2022), we also add the dummy variable 'election year' which reports whether a general election took place in a country in a given year (1 = Yes, 0 = No).Having reported on data and method, it is now time to test the validity of our hypotheses.(For descriptive statistics on all variables, see the Online Appendix, Table A3.)

Results
As can be seen in Figure 1, the results lend credence to some, but not all, of our expectations.The fitted, solid line suggests that the share of statements containing critique tends to be lower in countries with strong oversight institutions.This finding corresponds with Hypothesis 1a, which asserts that stronger oversight institutions decrease the likelihood of MPs expressing opposition as critique.However, the fitted, dashed line indicates that the share of statements containing alternatives is slightly higher in countries that have strong oversight institutions.Again, this result corresponds with our expectations because Hypothesis 1b suggests that stronger oversight institutions increase the likelihood of MPs expressing opposition as alternatives.
However, partly against our expectations, the two fitted lines in the scatter plot in Figure 2 indicate that Eurosceptic parties both express more critique and offer more alternatives than their Europhile counterparts.These results correspond with Hypothesis 2a, which asserts that MPs from more Eurosceptic parties are more likely to express opposition as critique.However, they do not lend support to Hypothesis 2b, which proposes that MPs from more Europhile parties will be more likely to express opposition as alternatives.To test whether these findings hold in a multivariate setting, we now present the results from the logistic regression.
Table 1 summarizes the results of the multivariate logistic regression.The odds ratio indicates the change in the odds of a statement expressing critique (Models 1 and 3) or offering alternatives (Models 2 and 4) as a result of a oneunit increase in the independent variable.Whereas an odds ratio greater than 1 indicates that a positive association exists between the independent variable and the outcome, an odds ratio smaller than 1 indicates a negative association.Finally, an odds ratio of 1 indicates that no association exists.By applying the simple equation 100 * (odds ratio -1), odds ratios can be transformed into percentage changes.Model 1 tests the effect of oversight institutions and attitudes towards European integration on the probability that a statement contains critique.Model 2 tests the same two variables concerning their effect on the probability that a statement offers alternatives.
The regression results provide strong support for Hypothesis 1a.Model 1 demonstrates that stronger oversight institutions reduce the probability of MPs expressing opposition as critique (p < 0.01).The odds ratio indicates that the odds that a statement contains critique decreases by 92.8 percent when made by an MP in a parliament with maximum institutional strength compared with an MP in a parliament that lacks oversight institutions.Conversely, against our expectations (Hypothesis 1b), strong parliamentary oversight institutions do not affect the probability of MPs offering alternatives, as can be seen in Model 2.
Turning to Euroscepticism's effect on the two types of opposition, the results only partially support our hypotheses.In line with our expectations (Hypothesis 2a), statements made by MPs from more Eurosceptic parties are more likely to contain critique than statements made by MPs from parties with more favourable views on European integration (p < 0.01).With a one-unit increase in the level of support for European integration, the odds of a statement containing critique decreases by 19 percent.However, MPs from Eurosceptic parties are also more likely to offer alternatives (p < 0.01).With a one-unit increase in party support for European integration, the odds of an MP making a statement offering alternatives decreases by 18.7 percent.These findings indicate that Eurosceptic parties dominate the exercise of all types of opposition, leading to a firm rejection of Hypothesis 2b.
By adding an interaction term to the prior specifications ('oversight institutions * EU position'), Models 3 and 4 test whether the effect of oversight institutions is dependent on party positions on European integration.Hypothesis 3a, suggests that the negative effect of stronger oversight institutions on the likelihood of MPs expressing opposition as critique is greater for Europhile parties than for Eurosceptic parties.In support of this proposition, Model 3 reveals that the effect of oversight institutions on opposition expressed as critique is, indeed, dependent on a party's position on European integration.Figure 3 plots oversight institutions' marginal effects on the probability that a statement contains critique, depending on the various party positions on European integration.As the level of Euroscepticism increases (with lower values on the x-axis), stronger oversight institutions' negative effect on the probability of MPs expressing opposition as critique diminishes (p < 0.01).However, Figure 4 reveals that oversight institutions' marginal effect on offering alternatives hardly changes with a party's position on European integration.Thus, we do not find support for Hypothesis 3b, which states that the positive effect of stronger oversight institutions on the likelihood of MPs presenting alternatives is greater for Eurosceptic parties than for Europhile parties.The interaction term does not reach any level of significance.Taken together, the results indicate that the strength of oversight institutions and a party's degree of Euroscepticism jointly function as significant determinants of the likelihood that MPs will express opposition in the form of critique.However, the same cannot be said when it  1.
comes to the likelihood of offering alternatives.Whereas the strength of oversight institutions fails to explain variation in the share of alternatives offered, the Euroscepticism level remains a significant predictor.
Only some of the control variables are significant throughout the model iterations.Unsurprisingly, all four models indicate that MPs from opposition parties are more likely to express critique and offer more alternatives than MPs from government parties (p < 0.01).However, neither the seat share nor the left-right position of the party to which an MP belongs are consistent predictors of opposition, either in the form of critique or alternatives.Moreover, concerning the arena, MPs are more likely to offer alternatives in the plenary context (p < 0.05), but the arena variable exerts no significant effect on the probability of MPs offering critique.The coefficients of the election year variable indicate that MPs are more likely to express opposition during election years, but with one exception only (Model 2) this effect is not statistically significant.
Finally, only a few of the policy area and country dummies are statistically significant (see the complete results in the Online Appendix, Table A6).Furthermore, we ran several robustness checks to ensure the validity of our results.First, we replaced our measure of a party's EU position with a binary variable that marked all parties as either Eurosceptic or mainstream  1.
(see the Online Appendix, Table A7).The resulting regression results reveal that stronger oversight institutions remain a significant driver that reduces opposition levels in the form of critique, but not in the form of alternatives (cf.Model 1).Unsurprisingly, Eurosceptic parties tend to express both more critique and alternatives, corresponding with the main results (cf.Models 1 and 2).Furthermore, the interaction effect of oversight institutions and EU party position remains significant for critique and insignificant for alternatives in our robustness checks (cf.Models 3 and 4).Thus, we can conclude that our main results are robust to the alternative operationalization.
Furthermore, we separated Winzen's index of oversight institutions into its two core componentsinformation rights and the strength of constraining institutionsand ran regressions with both as the main independent variable (see the Online Appendix, Tables A8 and A9).The results reveal that information-related institutions' strength is a significant predictor of opposition, as parliaments with more information rights tend to provide more opposition in the form of alternatives, but less opposition in the form of critique.A higher degree of Euroscepticism remains a significant predictor of both opposition types.However, the interaction effect of information-related institutions and EU position only reaches significance for opposition in the form of alternatives.Moving on to constraining institutions, the results indicate that MPs in parliaments that can impose stronger constraints on their governments tend to express significantly less critique, while the likelihood of offering alternatives does not change significantly.Yet again, the EU position remains significant throughout the model iterations.In stark contrast to the results attained by only examining information-related institutions, the interaction effect of constraining institutions and EU position is a significant predictor of opposition expressed as critique, but not of opposition in the form of alternatives.

Conclusions
In an era marked by widespread Euroscepticism and attacks on liberal democracy, it is timely and important to provide thorough examinations of political opposition.Whereas opposition scholarship has highlighted the importance of institutional factors for how much and what type of opposition we will find in parliamentary settings (Garritzmann, 2017;Kaiser, 2008), recent studies have demonstrated that party characteristics affect oppositional behaviour, including in EU politics, where Eurosceptic parties are key drivers of opposition in parliaments (Karlsson & Persson, 2022;Persson et al., 2019;Senninger, 2017).However, surprisingly little research has examined the combined effect of institutional setups and party characteristics on oppositional behaviour.To address this literature gap, we set out to examine the nexus of parliamentary institutions and party characteristics to understand oppositional behaviour in EU politics.Drawing on previous work that has demonstrated that party characteristics and institutional factors interact to shape parliamentary opposition (Hoerner, 2017;Tuttnauer, 2018), we contribute new knowledge through an examination that is comprehensiveas it includes deliberations over EU affairs in both the plenary and the EACand focusedas it targets oppositional behaviour, rather than the behaviour of opposition parties.Crucially, our study breaks new ground by introducing the key distinction between opposition in the form of expressing critique and presenting alternatives (cf.Garritzmann, 2017).This distinction has indeed informed some recent studies on parliamentary opposition (Karlsson & Persson, 2022;Persson et al., 2019), but these have not been aimed at examining institutional factors and party characteristics as drivers of oppositional behaviour.
The importance of introducing the distinction between critique and alternatives is illustrated by our results in connection with the first set of tested hypotheses.Hypothesis 1b is not supported because no statistically significant effect from oversight institutions' strength on MPs' propensity to express opposition in the form of alternatives is found.However, Hypothesis 1a does find support because we find that MPs in parliaments with weaker oversight institutions express more opposition in the form of critique than do their colleagues in legislatures with stronger oversight institutions.Thus, it seems that MPs primarily use opposition in the form of critique as an alternative tool for controlling the government in the absence of strong formal oversight mechanisms.This connection would have remained undiscovered had we not distinguished between the two forms of oppositional behaviour.This underscores the importance of engaging in fine grained empirical research in this area.
As expected, our findings indicate that MPs representing Eurosceptic parties express more opposition than MPs representing Europhile parties.This holds for opposition in the form of critique, as well as in the form of alternatives, since our data support Hypothesis 2abut not 2b which expected Europhile parties to dominate the presentation of alternatives.Simply put, Eurosceptic parties are masters of opposition both in terms of expressing critique and in terms of presenting alternatives.
Perhaps the most interesting finding is that our data support Hypothesis 3a, i.e., the association between strong oversight institutions and opposition in the form of critique is conditioned on party characteristics.However, Hypothesis 3b is rejected, which again proves the importance of distinguishing between opposition as critique and as alternatives.Our analysis indicates that MPs from Eurosceptic parties are much less likely to decrease their oppositional behaviour in contexts with strong oversight institutions compared with their colleagues from Europhile parties.Thus, whereas the latter group of MPs seems to view formal oversight mechanisms partly as a substitute for expressing opposition, Eurosceptic MPs continue to engage in oppositional behaviour even when strong oversight mechanisms are in place.These findings illustrate that we need to consider the interplay between institutional factors and party characteristics if we want to understand oppositional behaviour in EU politics.As it turns out, the same set of institutions appears to have different behavioural consequences for different types of parties.
Two mechanisms may explain the differences in oppositional behaviour between MPs representing Europhile and Eurosceptic parties.First, the fact that Eurosceptic parties' behaviour is dictated by a desire to gain attention and votes ( de Vries & Hobolt, 2020), rather than actually influencing the government's position (Hoerner, 2017), means that they have strong incentives to express opposition even in the presence of strong oversight mechanisms.Second, the successful use of oversight mechanisms, like issuing resolutions, means that a majority must back them in parliament.Whereas resolutions that mainstream parties issue generally have a good chance of being approved, resolutions that Eurosceptic parties issue are almost certain to be rejected (Hoerner, 2017).Thus, mainstream parties are in a much better position to utilize formal oversight mechanisms effectively than Eurosceptic parties.
While we could not provide the final word on the factors driving the differences in oppositional behaviour observed across the surveyed legislatures, we believe that our study makes two important contributions that should carry implications for future research on oppositional behaviour.
First, our results clearly demonstrate how crucial it is to distinguish between opposition through expressing critique and through presenting alternatives.As our study suggests, these different types of opposition do not follow the same behavioural logic.Oppositional behaviour in the form of expressing critique seems to be a substitute for strong oversight mechanisms, whereas oppositional behaviour in the form of presenting alternatives does not.It is noteworthy that our findings suggest that the alleged opposition deficit in EU politics (Karlsson & Persson, 2018;Rauh & de Wilde, 2018) is likely to be more pronounced in EU member states where parliaments enjoy strong oversight institutions, as the presence of such institutions reduces the incentives to express opposition in the form of critique.However, the problem in connection to the alleged opposition deficit is not an absence of critique, but rather an absence of more far-reaching opposition in the form of presenting alternatives to government policies.This form of opposition is so important because it provides the electorate with choice, which in turn is crucial if voters are to find voting meaningful.This key aspect of opposition is, as our results show, unaffected by the presence of strong oversight institutions.
Second, previous research has demonstrated that both institutional factors and party characteristics matter as drivers of parliamentary opposition (Tuttnauer, 2018), and that different types of party characteristics interact to shape oppositional behaviour (Hoerner, 2017).This study takes things one step further by establishing that institutional factors' effect on oppositional behaviour is conditioned on party characteristics.This finding highlights that more extensive comparative work will be required in the future if we are to get a more complete understanding of the drivers of oppositional behaviour in EU politics.

Figure 1 .
Figure 1.The strength of oversight institutions and the share of opposition expressed as critique/alternatives

Figure 3 .
Figure 3. Marginal effect of oversight institutions on the odds of a statement containing opposition in the form of critique, at different levels of Euroscepticism.Note: 95% confidence intervals.The plot is based on Model 3 inTable 1.

Figure 4 .
Figure 4. Marginal effect of oversight institutions on the odds of a statement containing opposition in the form of alternatives, at different levels of Euroscepticism.Note: 95% confidence intervals.The plot is based on Model 4 in Table1.