Voting Behavior, Coalitions and Government Strength through a Complex Network Analysis

We analyze the network of relations between parliament members according to their voting behavior.In particular, we examine the emergent community structure with respect to political coalitionsand government alliances. We rely on tools developed in the Complex Network literature to explorethe core of these communities and use their topological features to develop new metrics for partypolarization, internal coalition cohesiveness and government strength. As a case study, we focuson the Chamber of Deputies of the Italian Parliament, for which we are able to characterize theheterogeneity of the ruling coalition as well as parties specific contributions to the stability of thegovernment over time. We find sharp contrast in the political debate which surprisingly does notimply a relevant structure based on establised parties. We take a closer look to changes in thecommunity structure after parties split up and their effect on the position of single deputies withincommunities. Finally, we introduce a way to track the stability of the government coalition overtime that is able to discern the contribution of each member along with the impact of its possibledefection. While our case study relies on the Italian parliament, whose relevance has come into theinternational spotlight in the present economic downturn, the methods developed here are entirelygeneral and can therefore be applied to a multitude of other scenarios.