An empirical analysis of bill co-sponsorship in the U.S. Senate: The Tree Act of 2007

Public choice economists view the legislative process as a political market, in which interest groups attempt to influence the production of legislation that has pecuniary and non-pecuniary consequences for them; politicians provide these groups with relevant legislation. In this context, bill co-sponsorship acts as a signal to interest groups that a legislator is working to promote their interests and thereby maximize the payoffs received from such groups. In this paper we seek to identify factors associated with bill co-sponsorship, to determine whether interest group politics significantly explain bill co-sponsorship behavior in the U.S. Senate. Specifically, we examine Senate Bill 402, a bill seeking to amend the Internal Revenue Code of 1986 to allow a deduction for qualified timber gains. Senate co-sponsorship decisions concerning S.B. 402 are assessed using a model that identifies various political and industry (forestry) interests/characteristics. We demonstrate that a Senator's co-sponsorship of this bill is correlated with his/her seniority, tax-cutting ideology, strength of electoral victory in his/her most recent election, campaign contributions received from forestry interests, the relative contribution of forestry to Gross State Product, and the percent of total land in his/her state that is privately owned.