@inbook{NBERc10049,
 Crossref = "NBERgril84-1",
 title = "Tests of a Schumpeterian Model of R&D and Market Structure",
 author = "Richard Levin and Peter C. Reiss",
 BookTitle = "R & D, Patents, and Productivity",
 Publisher = "University of Chicago Press",
 pages = "175-208",
 year = "1984",
 URL = "http://www.nber.org/chapters/c10049",
}
@book{NBERgril84-1,
 title = "R & D, Patents, and Productivity",
 author = "Zvi Griliches",
 institution = "National Bureau of Economic Research",
 type = "Book",
 publisher = "University of Chicago Press",
 year = "1984",
 URL = "http://www.nber.org/books/gril84-1",
}