a1 Professor, Economics Department, University of Delaware, Newark, DE 19716, USA; and Research Associate, NBER. E-mail: grubbf@lerner.udel.edu. Web-page: http://myprofile.cos.com/grubbf16.
Footnotes
Preliminary versions were presented at SUNY-Binghamton and the 2007 NBER Summer Institute. The author thanks Kelly Lynn Perkins, Nathan Richwine, and Zachary Rose for research and Tracy McQueen for editorial assistance.