  We study the cohesion within and the coalitions between political groups in
the Eighth European Parliament (2014--2019) by analyzing two entirely different
aspects of the behavior of the Members of the European Parliament (MEPs) in the
policy-making processes. On one hand, we analyze their co-voting patterns and,
on the other, their retweeting behavior. We make use of two diverse datasets in
the analysis. The first one is the roll-call vote dataset, where cohesion is
regarded as the tendency to co-vote within a group, and a coalition is formed
when the members of several groups exhibit a high degree of co-voting agreement
on a subject. The second dataset comes from Twitter; it captures the retweeting
(i.e., endorsing) behavior of the MEPs and implies cohesion (retweets within
the same group) and coalitions (retweets between groups) from a completely
different perspective.
  We employ two different methodologies to analyze the cohesion and coalitions.
The first one is based on Krippendorff's Alpha reliability, used to measure the
agreement between raters in data-analysis scenarios, and the second one is
based on Exponential Random Graph Models, often used in social-network
analysis. We give general insights into the cohesion of political groups in the
European Parliament, explore whether coalitions are formed in the same way for
different policy areas, and examine to what degree the retweeting behavior of
MEPs corresponds to their co-voting patterns. A novel and interesting aspect of
our work is the relationship between the co-voting and retweeting patterns.
