@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", }