@inbook{NBERc11745,
 Crossref = "NBERirwi09-1",
 title = "Free Labor and Slave Labor",
 author = "Stanley L. Engerman and Robert A. Margo",
 BookTitle = "Founding Choices: American Economic Policy in the 1790s",
 Publisher = "University of Chicago Press",
 pages = "291-314",
 year = "2010",
 month = "December",
 URL = "http://www.nber.org/chapters/c11745",
}
@book{NBERirwi09-1,
 title = "Founding Choices: American Economic Policy in the 1790s",
 author = "Douglas A. Irwin and Richard Sylla",
 institution = "National Bureau of Economic Research",
 type = "Book",
 publisher = "University of Chicago Press",
 year = "2011",
 URL = "http://www.nber.org/books/irwi09-1",
}