Analyzing and Visualizing American Congress Polarization and Balance with Signed Networks

Signed networks and balance theory provide a natural setting for real-world scenarios that show polarization dynamics, positive/negative relationships, and political partisanships. For example, they have been proven effective for studying the increasing polarization of the votes in the two chambers of the American Congress from World War II on. To provide further insights into this particular case study, we propose the application of a framework to analyze and visualize a signed graph's configuration based on the exploitation of the corresponding Laplacian matrix' spectral properties. The overall methodology is comparable with others based on the frustration index, but it has at least two main advantages: first, it requires a much lower computational cost; second, it allows for a quantitative and visual assessment of how arbitrarily small subgraphs (even single nodes) contribute to the overall balance (or unbalance) of the network. The proposed pipeline allows to explore the polarization dynamics shown by the American Congress from 1945 to 2020 at different resolution scales. In fact, we are able to spot and to point out the influence of some (groups of) congressmen in the overall balance, as well as to observe and explore polarization's evolution of both chambers across the years.