Tracing the selection bias in roll call votes: party group cohesion in the European Parliament

Abstract

Legislative politics scholars rely heavily on roll call vote (RCV) data. However, it has been claimed that strategic motives behind RCV requests lead to overestimating party group cohesion and, thus, biased findings on legislative behaviour. To explore this claim, we distinguish between two types of bias, a 'behavioural bias' and a 'selection bias'. A recent rule change in the European Parliament, making RCVs mandatory on all final legislative votes, presents the unique opportunity to evaluate the latter. We compare party group cohesion in requested and mandatory RCVs by examining final legislative votes before and after the rule adoption using amendment RCVs (which still need to be requested) as a benchmark. The analysis shows that group cohesion is higher whenever RCVs are not just requested on some but mandatory on all votes. Hence, there is indeed a 'selection bias' in RCV data. Yet, somewhat contrary to former claims, relying on requested RCVs leads to underestimation of the cohesion party groups would have had were all votes automatically roll called. We argue that this is mainly because requests occur on more contentious votes.

Going on record: Revisiting the logic of roll-call vote requests in the European Parliament

“…Stated differently, contention in committee is a poor predictor of RCV requests. While previous studies (Finke, 2015;Yordanova and Mu¨hlbo¨ck, 2014) have suggested that RCV requests are biased towards contentious issues in plenary, this does not seem to be the case with committee decisions. This finding suggests that the nexus between decision-making in committee and voting in plenary may be imperfect (Yordanova, 2011: 609).…”

“…Indeed, there have been some notable interventions to the debate which have capitalized on this procedural reform to trace the selection mechanism (Hug, 2016;Yordanova and Mu¨hlbo¨ck, 2014). Therefore, one might argue that part of the theoretical puzzle of what is driving RCV requests is solved.…”

“…Therefore, one might argue that part of the theoretical puzzle of what is driving RCV requests is solved. Still, further investigating RCV requests may have its merits for two reasons: First, existing studies make claims about what motivates RCV requests by relying on quantitative data alone, usually focusing on revealed voting cohesion (Finke, 2015;Yordanova and Mu¨hlbo¨ck, 2014). Second, previous research has not taken into account the decision-making process at the committee stage.…”

Power versus Ideology: Political Group Switching in the European Parliament

“… Note that in the EP, not all votes are taken by roll call, which may lead to a selection effect. See Yordanova and Mühlböck () for a discussion and overview of the literature.…”

The influence of commissioners' characteristics on the EU's legislative process

“…Using the new rule on mandatory RCVs on final acts as intervention, Yordanova and Mühlböck (2015) showed that the cohesion of political groups is higher on all votes than was previously estimated based on requested RCVs. They argue that this shows that going on record was mostly requested on contentious issues.…”