@techreport{NBERw12829,
 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",
 institution = "National Bureau of Economic Research",
 type = "Working Paper",
 series = "Working Paper Series",
 number = "12829",
 year = "2007",
 month = "January",
 URL = "http://www.nber.org/papers/w12829",
}