@inbook{NBERc2233,
 Crossref = "NBERunkn61-1",
 title = "Factor Substitution and the Composition of Input",
 author = "Eric Schiff",
 BookTitle = "Output, Input, and Productivity Measurement",
 Publisher = "Princeton University Press",
 pages = "451-480",
 year = "1961",
 URL = "http://www.nber.org/chapters/c2233",
}
@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",
}