To use the whip or not: Whether and when party group leaders use disciplinary measures to achieve voting unity

Abstract

Party group leaders seemingly use a variety of disciplinary measures to achieve unified voting behavior in party groups. However, there is little systematic knowledge about the nature of such disciplinary measures and the interaction between leaders and group members remains a black box. Most studies of party voting concentrate on institutional variables such as electoral systems and take disciplinary measures as a given. This study presents a new way to measure party discipline, based on data from semi-structured interviews with 76 party group leaders and experts from five European parliaments. The discipline index provided here is the first to consider in a systematic way the means available to reprimand or reward party group members. In a second step, the study shows that disciplinary measures can compensate for a leader’s lack of control over candidate selection processes, and relate to group composition or size.

Keywords

Political parties party group discipline party group leaders voting unity cohesion

Introduction

When the German parliamentary party leader Volker Kauder threatened to dismiss his Christian Democrat colleagues from their committees after they refused to vote with their party group in a contested vote concerning the Eurocrisis, a heated debate developed regarding how frequent and usual such disciplinary measures are.¹ Allegedly, party leaders exert such pressure by means of various instruments in order to achieve the highest voting unity possible when party group members are in conflict with the party position when voting.² These instruments encompass threats (such as losing a parliamentary seat) or promises (such as being offered an attractive position). Apart from such anecdotes, we have very little systematic knowledge regarding the degree to which parliamentary party leaders use disciplinary measures to ensure voting unity³.

Several studies investigate the determinants of voting unity in parliaments, focusing particularly on the influence of electoral rules (Carey and Shugart, 1995; Depauw and Martin, 2009; Hix, 2004; Ohmura, 2014), nomination procedures (Hazan and Rahat, 2010), and party group attributes, such as group size, to explain high levels of voting unity (Carey, 2009; Coman, 2015; Sieberer, 2006).⁴ However, the disciplinary measures used by the leadership to achieve unity are rarely directly investigated and often simply assumed as given (Carey, 2009). It is widely expected that if ideological homogeneity is not sufficient to achieve voting unity, leaders resort to the use of disciplinary measures (Hazan, 2003). Disciplinary instruments such as ‘black books’ on financial and sexual misdemeanors of party group members and rewards such as promotions to higher positions (Martin, 2014) are examples of leaders’ attempts to ensure unity in parliamentary party groups (PPG) when group members disagree with the group line. However, examples such as these do not suffice as systematic evidence of disciplinary measures. This means that a critical question remains unanswered: when investigating high voting unity there is an observational equivalence between an ideologically homogeneous and very disciplined party so that we do not know which mechanisms lead to the high levels of voting unity, which we often observe in European party groups (Krehbiel, 2000: 222). As long as we have not looked inside party groups, it remains indeterminate where the voting unity comes from. From a normative perspective, more knowledge about the measures by which unity is achieved is however desirable because this factor can influence parliamentary decision-making and should, therefore, be open to public scrutiny (Heidar and Koole, 2000a).

In order to address this gap, this article develops a new way of measuring disciplinary actions and, with regard to 25 European party groups, analyses the determinants of their use, thereby generating a more systematic understanding of this element of legislative decision-making. Specifically, this study shows that party leaders use behavioral disciplinary tools especially in situations where party group leaders cannot select their group members during the nomination process ex-ante or when voters strongly influence the parliamentarians.

The first part of this study is exploratory in nature and inspects the kind of disciplinary instruments that are used. Particular attention is paid to the behavioral measures that are more difficult to assess and have been mostly neglected in prior research. These measures are summarized in an index, which is then used to investigate the influence these factors have on the degree of discipline in a second step. This correlation analysis in the second part of the study also serves as a validity test of whether the index displays the expected relationships with independent variables formulated in previous studies. The statistical analysis from the subsequent section shows that the use of disciplinary measures is a reaction to the lack of ex-ante selection mechanisms and the particular characteristics of the party group itself, including its ideological heterogeneity, and the percentage of constituency-oriented parliamentarians.

Why party group discipline is needed

Most analyses of European parliamentary systems have revealed a high level of voting unity within party groups (Depauw and Martin, 2009; Hix, 2004; Sieberer, 2006). Such a high level of unity can be brought about by ideological cohesion, institutions such as electoral and nomination rules (Sieberer, 2006), the confidence vote procedure (Coman, 2015; Diermeier and Feddersen, 1998), or party strength (Tavits, 2012).

Nevertheless, parliamentarians occasionally do defect from the party line, for reasons such as the representation of interests of other principals, for example, local voters (Tavits, 2009) or interest groups which may lead to ideological heterogeneity in the party group. The wish to stay individually accountable to the voters may undermine the ability of parties to ensure their collective accountability to the citizens, who desire a legislature that is able to act and take decisions in unison. In the political science literature, more attention has been paid to the accountability between voters and individual representatives, as for example in the representation literature (Powell, 2004), while comparatively less research has been dedicated to the question of how collective accountability between parties and voters is ensured. Possible mechanisms include shared norms and rules (Andeweg and Thomassen, 2011), but also the use of disciplinary measures by the party group leaders (Bowler et al., 1999).

By using disciplinary measures, the party group leaders solve the collective action problem of reaching a common decision, such measures may be regarded as an institutional solution for the control of party members in order to deliver the public good of decisions and ensure the party’s collective accountability towards the voters (Cox and McCubbins, 1994; Müller, 2000). To implement the interests of the voters and keep election promises, parties have to behave coherently and avoid defective behavior by rewarding those who cooperate and punishing those who do not (Cox and McCubbins, 1994). This task is often carried out by the party group leaders themselves, their executives, or specially created offices such as the party whips (Cowley, 2005; Raunio, 2000). Experts disagree over the extent to which disciplinary measures are used: while certain descriptive accounts for single countries (e.g. Cowley, 2005) and more analytical studies (see Kam, 2009; Sieberer, 2006) acknowledge and describe their existence, other studies state that sanctions are used less often than assumed (Andeweg and Thomassen, 2011; Willumsen, 2017). The empirical analysis below investigates, with the help of evidence from 76 interviews with members of 25 European party groups in five European parliaments, whether, and to what degree, disciplinary measures are undertaken. The results demonstrate that party leaders do deliberately use behavioral disciplinary tools to maintain discipline within their parties.

How party group discipline is exerted

The relationship between parliamentarians and their voters and party group leaders is often characterized as a ‘multiple principal problem’ since parliamentarians have to serve at least two principals: their voters, who want their opinions represented; and their party leaders, who want their parties represented (Carey, 2009). To prevent agency losses, for example, lost votes due to defections, the party group leader – as a principal – controls the PPG members through informal, internal party mechanisms or through the institutionalized parliamentary delegation chain (Müller, 2000: 319). The delegation chain provides the party group leadership with the means to control offices such as cabinet posts or committee memberships (Bowler et al., 1999: 10). More informal mechanisms include, for example, different forms of monitoring. Additionally, the regular party group sessions provide an opportunity for working on a unified party line and communicating dissenting positions to the party group (Raunio, 2000: 239). Further informal means of control include warnings or expulsion from the party group. Besides negative sanctions, positive instruments, such as the promise of attractive travels abroad (Baker et al., 1999: 74), more attractive office space or longer speaking time in parliament (Heidar and Koole, 2000b), are also at the disposal of the whips and leaders.

When party group discipline is used

Disciplinary measures are what could be considered as a ‘last resort’ instrument in the toolbox of the party group leader. The leader can punish a group member for not keeping to the party line only at the very end of the legislative representation chain. A much more efficient ex-ante tool available to the group leader is the selection of group members during the nomination process (Heidar and Koole, 2000b; Schattschneider, 1942). This capacity to select obedient group members gives the group leader much more control compared to systems in which the candidate is recruited by the local party committees (Reiser, 2014) or by an encompassing party selectorate, which includes many more people than the party group leadership (Hazan and Rahat, 2010). The mechanism employed for the selection of candidates for parliamentary seats therefore clearly influences party group members’ probability of following the group line. Necessarily, the use of behavioral disciplinary measures exerted in parliaments with less inclusive candidate selection rules will be lower because alreadyloyal members are much more likely to serve the party group. Therefore, I expect more disciplinary measures to be used when group leaders have little control over the nomination process. This mechanism also functions once candidates are elected: anticipating the influence of party group leaders on their re-nomination, members of parliament (MPs) take into account that their political destiny can be significantly shaped by their group leaders.

After being nominated and elected, parliamentarians are expected to represent the interests of their voters in order to get re-elected (Mayhew, 1974). If deputies consider it to be more beneficial to follow their voters’ views than their party’s when these opinions diverge, they tend to side with the voters rather than with the party. Parliamentarians who vote against the party line might enjoy higher levels of name recognition than their more loyal colleagues (Kam, 2009), with the result that strong local ties often lead to their defection (Tavits, 2009). This more or less direct-representation desire of parliamentarians is often related to their self-ascribed role as delegates of the citizens or to the greater or lesser personalization of the election system. I therefore expect that a strong influence on parliamentarians by the voters leads to the use of more disciplinary measures by the party group leadership.

In addition, the pure size of a party group is also expected to correlate with the degree of disciplinary measures used (Heidar and Koole, 2000a: 19). On the one hand, it could be argued that particularly small party groups are more concerned about appearing united since they are closer to the electoral threshold. Their existence might be at risk if they appear to be too heterogeneous. Moreover, smaller party groups might be younger than more established party organizations or might attract less institutionally committed members, so that they need more disciplinary efforts to work together. On the other hand, sociological studies show that larger groups have more complex dynamics which make it harder to provide the good of a united vote (Hackman and Vidmar, 1970). For example, more opinions in a party group require greater coordination efforts (Sieberer, 2006). Besides this, given that party groups are often subsidized according to their size, larger party groups tend to have more resources at their disposal with which they can influence their members (Raunio, 2000).⁵ Larger party groups are thus expected to use more disciplinary instruments.

The effect of the ideological heterogeneity of a party group is theorized in a similar way: the closer the ideologies of group members, the easier it is to maintain voting unity within the group. It is thus expected that leaders are likely to put ever greater pressure on their party group members if ideological positions are more spread.

Research design: Case selection and method

The choice to investigate the parliaments of Switzerland, Germany, the Netherlands, the United Kingdom and the European Union was motivated by the need to ensure sufficient variation regarding the relevant institutional variables drawn from the previous literature on voting unity (see a more extensive discussion on the case selection in the online appendix and table A1 in the online appendix found with the online article at ipsr@sagepub.com,).

Regarding the measurement of disciplinary measures, previous efforts include a study by Sieberer (2006), who measured disciplinary measures in terms of the services party groups can offer to their parliamentarians as indicated in parliamentary handbooks. Kam (2009), on the other hand, coded media information on individual incidences when party leaders punished dissenters. Although important initial steps in measuring discipline, elite interviews have the potential to reveal much more about these measures, particularly those which are not reported on in the media and those which are more subtle than can be accounted for by assessing the services granted to parliamentarians by the party group (please refer to table A2 in the online appendix, ipsr@sagepub.com and its description for a further discussion of the interview technique and the selection and distribution of interview partners).

It was remarkable that the party group leaders who were interviewed as part of this study admitted to using the mentioned instruments, since politicians usually insist that disciplinary measures do not exist citing the respective constitutional articles that state that parliamentarians are supposed to follow only their conscience. Even so, the party group leaders still reported a lower use of disciplinary measures compared to the experts. Hence, while the estimates of both the group leaders and experts are reported in the descriptive analysis below, the calculation of the index is based solely on the leaders’ possibly underestimated assessments, in order to use only the more conservative score.

The questionnaire included open and closed questions and was designed to capture all types of behavioral disciplinary measures mentioned in the existing literature on party group discipline (Bowler ei al., 2006) (please see the section ‘Question Wording’ and ‘Further Description of Questionnaire’ in the online appendix at ipsr@sagepub.com for a more extensive discussion on the questions). The four selected question items (committee assignment, opportunities for self-promotion, access to the media, and special benefits) were included in the index since their use was recognized and available in all of the five parliaments, indicated by the fact that the average score of use was closer to 1 (= very rarely) than 0 (= never) (see table A5 in the online appendix at ipsr@sagepub.com for the scores of the individual items according to parliament). Furthermore, the index only uses items which can, in principle, be used in all parliaments and are not dependent on the institutional system. That is the reason why, for example, the possibility of promoting someone to government was not included since this would only have been possible in three of the five parliaments under investigation. Moreover, there was variation in their use since if there had been no variation, it would not be interesting to add them to a common scale, since they would not contribute to the index (Steenbergen et al., 2003).

In addition to the interviews with party group leaders, online and mail surveys were conducted with all party group members of the five parliaments in the period 2006–2009.⁶ These questionnaires served to gather data on the independent variables used in the second part of the paper: ideological divergence; the candidate selection process; and the importance of the various principals, such as voters, for the parliamentarians.

Regarding the correlates of discipline such as ideological heterogeneity, we used the agreement index (Van der Eijk, 2001) based on the estimates of the Left–Right orientation of the parliamentarians in each party group as measured in the surveys. The desire to represent citizens was operationalized using the percentage of parliamentarians who answered that they would rather vote with the constituency than with the party group in case of a conflict of opinion between these two principals.⁷ To account for the centralization of the candidate recruitment process, the parliamentarians’ estimates regarding the importance of local party officials for their selection was used. These data were collected in our parliamentary surveys. The size of the party groups was measured as the percentage of seats held by a party group in the respective parliament (for more information see also tables A3 and A4 of the online appendix, ipsr@sagepub.com).

Findings

In the following section, I present the most common disciplinary behavioral measures in party groups. This descriptive evidence demonstrates that disciplinary measures are indeed used in spite of some experts claiming that this is not the case.

Committee assignment

Assuming that parliamentarians seek to work in committees in which they can best represent the interests of their constituency, or where they can use their expertise and gain the most prestige, the distribution of committee seats at the beginning of the legislature can be an efficient rewarding or sanctioning tool available to group leaders (Damgaard, 1995).

In all the parliaments investigated, the consideration of party group members’ loyalty before granting them a seat in a certain committee is a known instrument, as stated by both group leaders and experts. Leaders in all five parliaments assigned the use of this measure a 1.4 (= very rarely), whereas experts rated its use a bit higher, at 2.4 (= rarely). This difference reflects the possibility that party leaders might downplay the use of disciplinary instruments. There is some variance between parliaments in the use of this measure, it being known best in the House of Commons and the Bundestag, as the following quote illustrates:

Yes, we do that rather often. There is a competition for these seats. You rather take the loyal ones. (Party group leader, Bundestag)

The assignment of committee seats is also strongly influenced by other criteria, such as expertise and professional knowledge in a certain policy area, as well as seniority:

For the interesting commissions there are more applications than seats. The MPs are then chosen by involvement in the topic in the past, seniority and general behavior (that means if you are reliable). The distribution of seats is not as ‘cruel’ as your question is. The good ones get a seat, the bad ones certainly not. Influencing MPs by granting seats in interesting commissions happens very rarely. Everybody is conscious that it might happen, but it happens very rarely in reality. (Party whip, House of Commons)

In Switzerland and the European Parliament (EP), the use of this disciplinary measure is much less common: in the case of the latter, for example, the party leaders of the European People’s Party have much less say since this group agreed to distribute seats according to the D’Hondt rule, in accordance with national quota rather than loyalty.

Opportunities for self-promotion in parliament

Not as much knowledge exists about less-institutionalized disciplinary measures such as the granting of opportunities to parliamentarians to distinguish themselves in parliament. These measures are somewhat influenced by institutional possibilities: for example, in the EP, the Bundestag, the Swiss Parliament and the Tweede Kamer, the group leaders determine who is going to speak in parliament, in contrast to the House of Commons, where this is decided by the Speaker of the House (however, other self-promotion opportunities, such as assigning prestigious portfolios, are used in the UK instead). Thus, in all parliaments but the British one, leaders can use their authority to determine whether and for how long a parliamentarian speaks during TV recorded or otherwise prestigious sessions as a disciplinary instrument, as a German party group leader outlined:

Of course, you are only allowed to talk in the morning when Phoenix [public TV news channel] is reporting if you are a loyal party group member. The dissenters are only allowed at night. (Party whip, Germany)

However, relevant expertise and the activity of a parliamentarian are also considered:

Concerning the speaking time, our group favors MPs that have taken part in the discussions and have been present in the committee meetings. In the discussions before the plenary, our group tends to give more speaking time to the more active members. (Secretary-General of an EP party group)

Apart from speaking time, other tasks which allow for a demonstration of political skill are available in all party groups, and are used by all of the leaders interviewed to discipline their group members. The values for this measure are therefore relatively evenly distributed between party groups. In the case of the EP, party group leaders reward loyal or industrious members by assigning them special rapporteurships (see also Hurka and Kaeding, 2011), which is why the EP was assigned the highest score (1.9 when judged by the leaders and 3 when judged by the experts) in the category of self-promotion opportunities. Those group members who receive a rapporteurship are made responsible for presenting and taking care of a special legislation dossier, which gives them attractive opportunities to demonstrate their professional qualities:

Usually, you choose persons for rapporteurships who know a dossier and who have cooperated in the past. Of course, persons who do not follow the party line in the votes will not receive rapporteurships in the future. (Assistant of an EP party group leader)

Interestingly, the estimates for this disciplinary instrument differ quite substantially between party group leaders (average estimate of 1.3) and experts (2.6): whereas experts considered these instruments to be rather widespread, leaders were more reluctant to admit that they are used.

Access to the media

A measure related to the opportunity for self-promotion is the prospect of appearing in the media. Party group leaders can, to some extent, control access to the media, again giving them the opportunity to reward their more loyal group members (average estimate of 1 as judged by party leaders, 1.6 as judged by experts). The Swiss parliament and the EP (both 1.3) were assigned the highest values with regard to this measure, possibly because MPs from these two parliaments are competing for media attention with other political actors, for example, with national politicians in the case of the EP, so that media access is particularly highly valued. Examples concerning the use of media access as a reward include the following:

Certainly you give the media coverage rather to the ones that do their job. Further, if there is a party line, people that don’t follow the party line are not present in press campaigns. (Party group leader, EP)

You encourage but the media wants number one and then maybe another one. Because number one is not everywhere all the time, you want to push forward another one. We try [to place people in the media] but it is very difficult. (Party group leader, Tweede Kamer)

Party group leaders have a strong incentive to control access to the media since dissenters are very popular with the media but are harmful to the external appearance of the party:

For us, every parliamentarian is interesting who says something else than the party group leadership. (Parliamentary expert and journalist of a German weekly news magazine)

Sometimes the parliamentarians get so intimidated by the party group leadership that they say to us: ’I cannot tell you anything, it’s impossible. (Journalist specialized in German parliamentary affairs)

Benefits such as travel

Business trips or office space (e.g. in the House of Commons) are further special benefits which party group leaders can distribute to or keep back from group members. This measure is used in all parliaments and, according to party leaders themselves, is most common in the EP (score of 1.8). Apart from the Swiss People’s Party, which, due to its national orientation, does not consider the opportunity to travel as a reward, most group leaders are aware of this instrument:

This thought is always there. Who has earned to go to the EP or to California? Probably Kyrgyzstan in winter is less likely to be used as a reward, no one wants to go there. But if there are attractive travels, the rewarding certainly plays a role. (Swiss expert and former party group leader)

In the British case, however, some commented that sending members abroad is also used as a means of getting rid of outside opinions:

Sometimes we also nominate an MP for a delegation to get rid of this person. (Chief Whip, House of Commons)

Apart from business trips, tickets to certain sports events or office space were also cited as possible rewards by the group leaders.

Additional instruments

The interviews revealed that a couple of additional means exist. These instruments are mostly in the form of monitoring and oversight tools in that they facilitate close contact and intense communication between the group members and the party group leadership. They range from particular monitoring mechanisms, such as the establishment of voting records (e.g. the Liberal party group ALDE has been amongst the first EP party groups to systematically record the votes of their members), to intense talks with the leadership:

They try to argue and convince them. It is a lot about convincing people. Having a meeting with the Prime Minister, that is a ‘big meeting’. (Whip, House of Commons)

[Before the vote] the party group leadership sent SMSs [short message services] to a dissenter during the whole night. They ‘treated’ him constantly. (Expert, Bundestag)

In particular in the European and the Swiss Parliaments, such monitoring and attempts at professionalization have increased, suggesting that these parliaments are becoming more like the more established parliaments (Bailer and Bütikofer, 2015).

An index of disciplinary measures and how their use can be explained

When using the interview estimates to create a discipline index, the difficulty lay in the fact that the parliamentary experts had less of an incentive to hide information but were rarely able to distinguish between party groups due to a lack of insider knowledge. In most cases, they could convincingly outline which means were used to what degree in the parliament in question, but they could at most distinguish between parties in government/opposition or big/small parties. The party group leaders themselves were well able to judge how often the various means are used in their own party group; however, they had an incentive not to be too honest. Furthermore, they could not judge the use of disciplinary instruments in the other party groups. In view of these observations, I opted for the leaders’ estimates to build the index, in order to base it on the more conservative scores as well as to obtain ratings for the individual party groups.

To create a measure for the overall use of disciplinary instruments, an additive index was composed of the individual measures for committee assignment, opportunity for self-promotion, access to the media, and special benefits such as travel. Using a Mokken scaling procedure, I investigated whether the questions measure the same constructs, and for all items a sufficient scalability of a Loevinger’s H coefficient above 0.3 was achieved (Hardouin et al., 2004). Using polychoric correlations, I also tested how strongly the individual items are correlated amongst each other, which indicated that the lowest correlation is between special benefits and committee assignments (0.35), and the highest between media access and opportunities for self-promotion (0.7). A factor analysis indicated one distinct factor with an eigenvalue above 2. Hence, it would also have been possible to use the resulting factor as the dependent variable. This factor correlated with the additive index with a coefficient of 0.99, but I nevertheless decided to use the additive index. Besides being more intuitive, adding the items also means that the individual items are substitutable: if a party group leader makes less use of one item, such as controlling access to the media (e.g. in the British Labour Party), he is able to use special benefits, such as attractive delegations, as a substitute. There is no indication in the literature that one item is more important than the others, since we only have anecdotal knowledge about disciplinary measures so far. Therefore, the items are aggregated with equal weight (for further details, please see the section ‘Further description of discipline index and robustness tests’ in the online appendix).

When looking at Table 1, which displays the index values by party group, the group of parties that do not use any behavioral disciplinary measures becomes apparent. These are mostly small opposition parties, which are rarely in government and thus not in a position to influence, and thus also less relevant, for the passing of laws in a legislature. Furthermore, these are often groups of only five to eight people, making coordination much easier than in the larger party groups.

Table 1.

Discipline index.

Party group and parliament	Party family	Discipline index
ALDE-EP	Liberal	10
FDP-DE	Liberal	9.5
SP-EP	Social Democrat	9.5
CVP-CH	Christian Democrat	8.3
VVD-NL	Liberal	8
Labour-UK	Social Democrat	7.3
PvdA-NL	Social Democrat	6.8
EVP-EP	Christian Democrat	6.5
SP-CH	Social Democrat	6
Green-DE	Green	6
SVP-CH	Conservative	4.7
FDP-CH	Liberal	4.5
CDA-NL	Christian Democrat	4.5
Liberal D	Liberal	4
CDU-DE	Christian	3.5
Conservative-UK	Conservative	3
Green-CH	Green	2
SPD-DE	Social Democrat	1.5
EDU-CH (Conservative); SP-NL (Social Democrats); Linke-DE (Left); Groen-Links-NL (Greens); ChristenUnie (NL); D66-NL (Liberal); Green-EP (Greens); UEN-EP (Anti-European Union)		0

Generally, EP party groups have a surprisingly high discipline index, with an average value of 5.2, followed by the UK (4.7), Swiss (4.2) and German (4.1) parliaments. The Dutch parliament (2.8), on the other hand, displays a distinctly lower value. The results show that there is variance between parliaments and party groups, which justifies an analysis of the above-discussed factors to explain the different degrees of disciplinary measures applied.

As outlined by Zeller and Carmines (1980), social scientists usually investigate new scales by examining the empirical relationships between the measure and other variables with which it is expected to correlate. In this regard, Heath and Martin (1997) point out that these are rarely alternative measures of the same construct, so that the relationships are not expected to be strong. In this study, I test to what extent the discipline index correlates with variables with which it is expected to co-vary from a theoretical point of view. If the results indicate significant correlations, this can be taken as further evidence that the index successfully captures the behavioral aspect of party group discipline, which it was initially designed to measure.

I used ordinary least squares regression analyses with robust standard errors to correct for possible heteroskedasticity problems. Due to the low number of cases, I investigated the individual hypotheses in bivariate models only. The correlates of the disciplinary measures are listed in Table 2.⁸

Table 2.

The correlates of disciplinary measures (ordinary least squares regression analysis with robust standard errors).

	Decentralized nomination	Constituency orientation	Party groupsize	Ideological heterogeneity
Importance of local party officials for nomination	1.47*
Importance of local party officials for nomination	(0.76)
% of members of parliament who vote with constituency rather than with parliamentary political groups (PPG)		0.06*
		(0.03)
Size of PPG in % of seats			0.08*
			(0.04)

Left–Right Agreement Index				−11.96*
				(6.82)
Constant	0.44	2.86***	2.81**	13.73**
	(1.90)	(0.96)	(1.23)	(5.01)
Observations	19	26	24	23
R²	0.17	0.11	0.10	0.12
F	3.77	3.60	4.01	3.07

Note: Standard errors in parentheses.

p < 0.10; **p < 0.05; ***p < 0.01.

Concerning the candidate nomination rules, I find the expected positive effect, meaning that the more inclusive the selection process, the higher the discipline index. Since measuring candidate selection is notoriously difficult, given that it varies according to party, country and sometimes federal level, I asked the parliamentarians about the importance of regional party officials for their selection as candidates. This measure turns out to be positive and significant. The use of ex-post disciplinary measures is thus higher when party group leaders have less control ex-ante over the selection of candidates, as shown in the Dutch party system, which has the most inclusive candidate selection procedure with central party lists in the sample (Hazan, R and Voerman, 2006). A dummy variable accounting for the Dutch parliament has a strong negative effect with a coefficient of −1.79, but it is not significant at conventional levels (results not listed here). These results confirm that the use of disciplinary measures is more intense when party group leaders have less control over the ex-ante selection of candidates, as in the federal systems of the EP, Switzerland and Germany. This is confirmed by some of the party group leaders in the European and Swiss parliaments, who voiced a desire for this sort of selection control:

I wish I had the possibility to select my candidates. (EP party group leader)

Additionally, nearly all Dutch party group leaders confirmed in the interviews that they try to influence the candidate selection process, which is simply not possible in the other parliaments due to their decentralized nomination processes. As one Dutch party group leader outlined:

The political leader of course wants to influence, but officially, in my own party he has only the right to advise, there is no veto right or whatsoever. […] Of course, informally there is more influence.

An effect of voters on the extent of disciplinary measures used, as suggested in the second theoretical expectation, can also be confirmed. The larger the percentage of parliamentarians who vote in line with their constituency rather than with their party group, as measured by parliamentary surveys of all parliaments and party groups, the more disciplinary measures are employed. Often, party group leaders consider individual votes against the party group as an attempt to acquire immediate media popularity since journalists ‘celebrate the rebel’ (German civil servant of the parliamentary services). Simulating the effect using ‘clarify’ (King et al., 2000), I find that the discipline index has a value of 3.21 if the representation orientation is at its minimum value (as, for example, for the Christian Democrats in the Netherlands), keeping all other variables constant at their mean. On the other hand, the index goes up to 6.82 and higher if there is a large percentage of parliamentarians favoring the constituents instead of the party group (as, for example, amongst the Christian Democrats in Switzerland).

A positive and significant correlation between party group size and the use of disciplinary measures was found in the next model, confirming the expectation that increased coordination efforts, and thus more disciplinary efforts, are required in a larger party group. This confirms findings by Coman (2015), who found that larger party groups have a higher voting unity since they have better access to resources with which they can control the ‘agent’ MP. A liberal party group whip in the EP explained this as follows:

As the group increased in the 1990s, the discipline had to increase too. In a small group it is a kind of family affair, but in a big group, fights in delegations and between delegations start.

A member of the party group leadership of the Liberal Democrats in the House of Commons outlined the influence of the size of a party group as follows:

The only reason to change our current whipping system would be the size of the group. Out of the three main parties in Great Britain, the Liberal Democrats are the party that is the least rebellious. The main reason for this unanimous voting behavior is because everybody has the opportunity to express their own opinion and listen to other points of views.

When size is used as a control variable in the other models, all other independent variables become insignificant at conventional standards, which shows that size covers many of the underlying and relevant concepts, for example, heterogeneity (the correlation coefficient between heterogeneity and size is −0.58).

As suggested in the literature, a party group leader needs to exert more discipline when the party group is ideologically more heterogeneous. Indeed, the more agreement there is in a party group, the fewer disciplinary measures are employed, as the negative and rather large coefficient shows. Particularly in the EP, the need to unite the different parties in large party groups demonstrates this well, as a member of the party group leadership of the largest party group explained:

The biggest party groups have the biggest problems.[…]. However, it is not so much the size but the need to unite 40–50 different national parties.

I also controlled for the effect of government status, since this factor is discussed in previous studies. While Hix et al. (2007) found for the EP, that the deputies of parties represented in national government contribute to higher party group unity, Depauw (2003) observed that discipline is not necessarily higher amongst government parties. I was able to identify a positive but insignificant effect of parties in government (result not displayed), with the discipline index for governing parties standing at 4.7 and 3.6. However, the EP party groups were not included in this analysis since they can never be part of a government. An extension of this study would necessitate the inclusion of more points in time and more party groups from parliamentary systems.

Conclusion

There has so far been no systematic measure for the behavioral disciplinary tools used in party groups. The present study addresses this gap by presenting a first measure of discipline and explains its use with regard to 25 party groups in five European parliamentary systems. Using interviews, expert data, and parliamentary surveys, it shows that the use of behavioral disciplinary measures is a reaction to a lack of leadership control over the candidate selection procedure and that they vary according to the composition of the party groups as well as their size. In countries where national party group leaders can determine candidate lists, as in the Netherlands, fewer punishment and reward tools are applied. Considering the large number of elite interviews involved, substantial resources would be needed to create an index for other parliaments and party groups. However, the study can be used to develop a deeper understanding of the dynamics between party group leaders and their members. For other parliamentary systems and party groups, we can predict that disciplinary measures in party groups are not simply anecdotes but vary systematically according to the influence of the party group leader at the candidate selection stage and the characteristics of the party group.

Based on this first descriptive demonstration of the existence of various disciplinary instruments as well as the subsequent analysis of the correlates of party group discipline, this study adds to a lively debate in legislative politics about the functioning of party groups and contradicts party group leaders and scholars who claim that no disciplinary measures are used. The discipline index is a step towards specifying a concept that most legislative scholars assume to exist, but few know in what form and to what extent. It opens up the black box of interactions between party group leaders and their members and suggests that voting unity is not only a result of ideological cohesion or legislative norms, but that leaders actively try to influence this process in order to increase unity.

Footnotes

Acknowledgements

I thank Tamaki Ohmura and Silvia Matter for valuable research assistance; Patricia Buser, Slavena Georgieva, Elisa Ravasi, Maëve Romano, Nicole Staubli, for interview transscriptions, as well as the editors and reviewers of IPSR and Sarah Binzer Hobolt, Scott Desposato, Bjørn Høyland, Simon Hug, Heike Jüngst, Christopher Kam, Heike Klüver, Amie Kreppel, Shane Martin, and David Willumsen for valuable comments and suggestions, Furthermore I thank my interview partners for their time and expertise.

Funding

This research was supported by the Swiss National Science Foundation under grant number 101512-116617.

Notes

Author biography

Stefanie Bailer is professor of political science at the University of Basel. Her research interests encompass decision-making at the European and international level, parliamentarians and parliamentary careers in Western European parliaments, and negotiations in the European Union and international organisations. She has published in International Political Science Review, Political Studies, Review of International Organizations, Journal of Common Market Studies, European Union Politics, Journal of Legislative Studies and the Journal of European Public Policy.

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