Claims that the United States Congress is (becoming more) polarized are widespread, but what is polarization? In this paper, I draw on notions of intergroup relations to distinguish two forms. Weak polarization occurs when relations between the polarized groups are merely absent, while strong polarization occurs when the relations between the polarized groups are negative. I apply the Stochastic Degree Sequence Model to data on bill co-sponsorship in both the U.S. House of Representatives and U.S. Senate, from 1973 (93rd session) to 2016 (114th session) to infer a series of signed networks of political relationships among legislators, which I then use to answer two research questions. First, can the widely reported finding of increasing weak polarization in the U.S. Congress be replicated when using a statistical model to make inferences about when positive political relations exist? Second, is the (increasing) polarization observed in the U.S. Congress only weak polarization, or is it strong polarization? I find that both chambers exhibit both weak and strong polarization, that both forms are increasing, and that they are structured by political party affiliation. However, I also find these trends are unrelated to which party holds the majority in a chamber.
Neal, Z. P. (2020). A sign of the times? Weak and strong polarization in the U.S. Congress, 1973–2016. In Social Networks (Vol. 60, pp. 103–112). Elsevier B.V. https://doi.org/10.1016/j.socnet.2018.07.007