The Effects of Independent Expenditures in Senate Elections

Independent expenditures are designed to influence the preferences and behavior of the electorate. Like candidate expenditures, the money is generally spent trying to persuade voters to act a certain way on election day. Because of the continuous nature of the spending, the sophisticated techniques of influence it buys, and the absence of accountability, there is good reason to believe these expenditures are important determinants of the vote. Expenditures for the incumbent and against the challenger should help the incumbent, and expenditures for the challenger and against the incumbent should help the challenger. Using individual-level survey data, we develop a model of Senate vote choice that considers these independent expenditures as both exogenous and endogenous to the process. We then estimate this model in the 1984, 1988, 1990, 1992, and 1996 elections. We find that independent expenditures can significantly affect vote choice, especially when modeled as endogenous to the process. These effects depend, however, on the electoral context, the type of independent spending, and the type of candidate. In general, our results seem roughly to conform to the conventionally accepted account of the 20-year history of independent expenditures in U.S. elections.