Political Interaction in the Senate: Estimating a Political “Spatial” Weights Matrix and an Application to Lobbying Behavior

Many motivations exist that cause legislators to behave strategically when voting. However, it is difficult to uncover the magnitude of the interaction among politicians. This paper takes a “spatial” approach to the problem, using a spatial autoregressive model where the elements of the spatial weights matrix are estimated as parameters. The political spatial weights matrix is calculated for 96 senators in the U.S. 110th Congress. Furthermore, I calculate the overall effect on voting from “flipping” a senator’s vote. I apply these measures to study political fundraising, mildly suggesting that political interest groups direct donations to senators with the most influence.