@techreport{NBERw13059,
 title = "Changing Progressivity as a Means of Risk Protection in Investment-Based Social Security",
 author = "Andrew A. Samwick",
 institution = "National Bureau of Economic Research",
 type = "Working Paper",
 series = "Working Paper Series",
 number = "13059",
 year = "2007",
 month = "April",
 URL = "http://www.nber.org/papers/w13059",
}