A Panel Probit Analysis of Campaign Contributions and Roll-Call Votes

Despite numerous analyses of the relationship between campaign contributions and the roll-call voting behavior of members of Congress, we still lack definitive answers to longstanding questions about whether contributions affect votes. Part of the reason for this is that it is methodologically difficult to account for members' predispositions to vote in favor of PACs' interests. This article seeks to advance our understanding of the relationship between campaign contributions and voting behavior by using a method for panel data that overcomes the problem of accounting for voting predispositions. This method enables us to account for individual specific effects, such as the predisposition to vote for or against a particular piece of legislation, which are too costly or impossible to measure. Applying this method, I find that contributions do not have consistent effects that would indicate that PACs are significantly biasing congressional decision making in their favor. he influence of "special interests" in politics is a perennial concern of those who seek to reform the political system in the United States. One way that special interests are perceived to have an undue influence is through campaign contributions. Efforts to reform campaign finance laws have been motivated in part by the belief that campaign contributions have a pernicious effect on the behavior of politicians. A recent Gallup survey found that 53 percent of individuals thought that campaign contributions influenced the policies supported by elected officials "a great deal" and 76 percent and 81 percent favored placing limits on contributions from labor and business groups, respectively (Saad 1997). Researchers have devoted a substantial amount of effort and resources to systematic analysis of campaign finance in order to uncover the relationship between campaign contributions and political decision making. One of the key questions that researchers have asked is "Do campaign contributions by political action committees (PACs) influence the roll-call voting behavior of members of Congress?" Despite numerous published analyses of contributions and votes, this question remains unsettled because of the conflicting answers that these analyses have produced.' Some studies have found no relationship between votes and contributions, while others have found the kind of relationship that reformers worry about. Part of the reason for these mixed results is that methodological problems have hampered attempts to assess accurately the degree to which PAC contributions affect voting. One of the most vexing problems is that it is difficult to untangle the effect of contributions from the effect of a member's predisposition to vote one way or another. That is, PACs contribute to members of Congress who are likely to vote the way the PACs favor even in the absence of contributions. A PAC donation to a friendly member might be misconstrued as