This report relied on the assistance, advice and published work of many people. In addition to those mentioned and quoted in the text, the authors would like to thank, in particular, Nigel Chalk, Jason Furman, Douglas Holtz-Eakin, Timothy Haynes, Glenn Hubbard, Arvind Krishnamurthy, Rohit Kumar, John Schreck, Chima Simpson-Bell, Michelle Smith, Chad Syverson, Eric Van Nostrand, Paul Winfree and Felicia Wong.