@inbook{NBERc10487,
 Crossref = "NBERaesm76-4",
 title = "Introduction to "Annals of Economic and Social Measurement, Volume 5, number 4"",
 author = "James J. Heckman",
 BookTitle = "Annals of Economic and Social Measurement, Volume 5, number 4",
 Publisher = "NBER",
 year = "1976",
 month = "October",
 URL = "http://www.nber.org/chapters/c10487",
}
@book{NBERaesm76-4,
 title = "Annals of Economic and Social Measurement, Volume 5, number 4",
 author = "Sanford V. Berg",
 institution = "National Bureau of Economic Research",
 type = "Book",
 publisher = "NBER",
 year = "1976",
 URL = "http://www.nber.org/books/aesm76-4",
}