@inbook{NBERc0881,
 Crossref = "NBERbern07-1",
 title = "International Comparisons of R&D Expenditure: Does an R&D PPP Make a Difference?",
 author = "Sean M. Dougherty and Robert Inklaar and Robert H. McGuckin and Bart van Ark",
 BookTitle = "Hard-to-Measure Goods and Services: Essays in Honor of Zvi Griliches",
 Publisher = "University of Chicago Press",
 pages = "291-322",
 year = "2007",
 month = "October",
 URL = "http://www.nber.org/chapters/c0881",
}
@book{NBERbern07-1,
 title = "Hard-to-Measure Goods and Services: Essays in Honor of Zvi Griliches",
 author = "Ernst R. Berndt and Charles R. Hulten",
 institution = "National Bureau of Economic Research",
 type = "Book",
 publisher = "University of Chicago Press",
 year = "2007",
 URL = "http://www.nber.org/books/bern07-1",
}