Analyzing the Political Divide using Graph Theory
In the past decade, the United States political system has been claimed to be polarized: divided between social constructs such as the state versus church or worker versus owner, but is there a mathematical way to confirm this division? In Parigi and Sartori’s research paper titled “The political party as a network of cleavages: Disclosing the inner structure of Italian political parties in the seventies,” Parigi and Sartori utilize network concepts to reason about the divide within Italian political parties in the seventies.
Much of their work relies on the assumption that interactions between nodes (parliamentary members) are classed as strong and weak ties. In their network model, parliamentary members who repeatedly cosponsor bills are considered strongly connected i.e. their edge between their nodes has a strong tie, while single instances of cosponsoring are considered a weak tie.
As seen in the following diagram, each node is a member of parliament (MP), and the entire graph is connected implying this graph is one large component. As mentioned by the researchers, this might pose a challenge to whether cosponsoring is a “good measure of formal and informal coalitions within each party” since it “may be the case that the large component of Fig. 2 is the result of political processes occurring externally to each part, rather than inside them.” Nonetheless, it is clear that this diagram reveals a clear clustering of nodes amongst the parties with the Fascist MSI party as the “most cohesive group.”
Furthermore, the researches examined the inner structure of two parties DC and PCI. They then mapped the effect of “cleavages” i.e. social issues that divide the population. The following diagram illustrates this clustering. It is very interesting that within a certain political party there exists multiple distinct social groups, yet these MPs would still cooperate and cosponsor certain bills together.
I believe this analytical framework can be extremely useful in studying many political systems including the United States. I believe it is necessary to quantify how separate or divided our country is. The effect of visualizing the network gives you a very clear understanding of the connections between party members that one can not quite grasp seeing just descriptive statistics.
Main Source: https://www.sciencedirect.com/science/article/pii/S0378873312000536 (To access this academic journal, you can login through Cornell and it is free!)
Additional Source: https://www.people-press.org/2014/06/12/political-polarization-in-the-american-public/