@inbook{NBERc2222,
 Crossref = "NBERunkn61-1",
 title = "Data Available for the Measurement of Output per Man-Hour",
 author = "Leon Greenberg",
 BookTitle = "Output, Input, and Productivity Measurement",
 Publisher = "Princeton University Press",
 pages = "147-200",
 year = "1961",
 URL = "http://www.nber.org/chapters/c2222",
}
@book{NBERunkn61-1,
 title = "Output, Input, and Productivity Measurement",
 author = "The Conference on Research in Income and Wealth",
 institution = "National Bureau of Economic Research",
 type = "Book",
 publisher = "Princeton University Press",
 year = "1961",
 URL = "http://www.nber.org/books/unkn61-1",
}