Over the past few years, the United States Congress has taken up some of the most important debates in decades. And as time has gone on, arguments over Coronavirus stimulus packages, impeachment, and Supreme Court confirmations have become increasingly polarized. From an outside perspective, Democrats and Republicans seem to really struggle to work together on anything. Whenever a bill gets introduced, responses to it always seem to be split along party lines. But is this worse than usual? Is the Congress of the United States actually currently more polarized than it has been previously? By analyzing the way members of Congress vote, we might be able to determine how deeply ingrained the partisan divide truly is.
To determine how divided Congress is, we need a way to measure how individual politicians relate to each other. We decided that the best way to do this was to analyze voting records. Getting data from VoteView, we were able to filter out how each Senator voted on each bill. We then established a network matrix where senators were the nodes and the edges between them were votes, weighted by how often the two senators voted together and filtered so that only pairs of senators who voted with each other on more than the median amount would retain an edge. We also were then able to timestamp the data by Congress so that we could analyze the change in the voting patterns over time.
The first method of analysis that we will apply to the matrix of shared votes, will be a singular value decomposition(SVD). We will use this to determine how far distinct voting patterns are. By taking the 1st and 2nd left singular vectors of each Congresses voting matrix, we are able to find the two vectors that best define how senators vote. After projecting senators onto these vectors, we can see how each individual senator is clustered on these axes of voting.