Does party loyalty in roll call votes influence re-nomination in parliamentary democracies?

In parliamentary democracies, the party leadership controls access to parliamentary and executive offices as well as candidate selection and therefore re-nomination. According to standard rational choice approaches, the party leadership accomplishes high levels of party unity by promising positive incentives to their parliamentary party group’s members of parliament (MP) and threatening with negative incentives. In terms of re-nomination, the literature assumes loyal members of parliament to be rewarded with promising list positions, while disloyal MPs should be punished with worse list positions or denied re-nomination. Although this assumption is central to the explanation of systematic variance of party unity induced by party discipline, empirical research on this subject has been surprisingly scarce so far. In order to test whether legislative behavior is reflected in party leadership decisions about re-nomination, we combine data on roll call voting of German Bundestag MPs from 1990 to 2017 with a novel dataset on re-nomination that also includes MPs who completely failed to regain nomination. Covering seven legislative periods, we are able to study the research question more extensively than existing research. Moreover, previous studies primarily focus on parliamentary speeches as indicator of party loyalty, which is problematic for several reasons. Party leaderships control access to the floor and therefore hinder disloyal members from expressing their discontent in publicly very visible speeches. Moreover, legislators usually only speak about their domain of expertise in parliament, which naturally leads to different vocabulary and therefore might distort quantitative measurement methods like wordscore. Roll-call votes are also publicly visible but in contrast to speeches, every MP is able to express her discontent with the party line on every topic in roll-call votes. Therefore, using this kind of legislative behavior as indicator of parliamentary party loyalty enables us to approach the research question on a broad scale. Furthermore, we include the full variance of re-nomination outcomes in our dependent variable. Besides easily measurable outcomes (better, same, worse list position), we have also collected data on involuntary re-nomination failures by an extensive media research. The latter cases were simply dismissed in previous analyses, although these are the most drastic cases of party leadership intervention and therefore the most interesting ones. By analyzing differences between parties under control of several structural factors like government status, office holding, seniority and gender, the empirical results enhance our understanding of both intra-party candidate selection and parliamentary party loyalty as well as, most importantly, the connection between the two. We find that the expected relationship between defection from the party line in roll call votes and reselection exists only in government parties. Because there is high variance in government composition during our observation period and we do not find clear party effects, we are confident to ascribe the effect to government status. This empirical finding has broader implications for the literature on ex ante/ex post control mechanism for party unity in other countries and in general.