@inbook{NBERc11143,
 Crossref = "NBERcard93-1",
 title = "Introduction to "Small Differences That Matter: Labor Markets and Income Maintenance in Canada and the United States"",
 author = "David Card and Richard B. Freeman",
 BookTitle = "Small Differences That Matter: Labor Markets and Income Maintenance in Canada and the United States",
 Publisher = "University of Chicago Press",
 pages = "1-20",
 year = "1993",
 month = "January",
 URL = "http://www.nber.org/chapters/c11143",
}
@book{NBERcard93-1,
 title = "Small Differences That Matter: Labor Markets and Income Maintenance in Canada and the United States",
 author = "David Card and Richard B. Freeman",
 institution = "National Bureau of Economic Research",
 type = "Book",
 publisher = "University of Chicago Press",
 year = "1993",
 URL = "http://www.nber.org/books/card93-1",
}