@inbook{NBERc0064,
 Crossref = "NBERpote06-1",
 title = "Introduction to "Tax Policy and the Economy, Volume 20"",
 author = "James M. Poterba",
 BookTitle = "Tax Policy and the Economy, Volume 20",
 Publisher = "The MIT Press",
 year = "2006",
 month = "September",
 URL = "http://www.nber.org/chapters/c0064",
}
@book{NBERpote06-1,
 title = "Tax Policy and the Economy, Volume 20",
 author = "James Poterba",
 institution = "National Bureau of Economic Research",
 type = "Book",
 publisher = "The MIT Press",
 year = "2006",
 URL = "http://www.nber.org/books/pote06-1",
}