[1
]Department of Economics, University of California-Davis, One Shields Avenue, Davis,
CA 95616, and NBER (email: )
[2
]Department of Economics, Texas A&M University, 3087 Allen Building, College Station,
TX 77843, and NBER (email: )
[3
]Department of Economics, Southern Methodist University, 3300 Dyer Street, Dallas,
TX 75275, and NBER (email: )