@inbook{NBERc7251,
 Crossref = "NBERgrub99-1",
 title = "Social Security and Retirement in Germany",
 author = "Axel Borsch-Supan and Reinhold Schnabel",
 BookTitle = "Social Security and Retirement around the World",
 Publisher = "University of Chicago Press",
 pages = "135-180",
 year = "1999",
 month = "January",
 URL = "http://www.nber.org/chapters/c7251",
}
@book{NBERgrub99-1,
 title = "Social Security and Retirement around the World",
 author = "Jonathan Gruber and David A. Wise",
 institution = "National Bureau of Economic Research",
 type = "Book",
 publisher = "University of Chicago Press",
 year = "1999",
 URL = "http://www.nber.org/books/grub99-1",
}