Shipan, Charles R.; Lowry, William R. (June 2001). „Environmental Policy and Party Divergence in Congress“. Political Research Quarterly. 54 (2): 245–63. doi:10.1177/106591290105400201. JSTOR449156.
Shipan, Charles R.; Lowry, William R. (June 2001). „Environmental Policy and Party Divergence in Congress“. Political Research Quarterly. 54 (2): 245–63. doi:10.1177/106591290105400201. JSTOR449156.