@techreport{NBERr1694,
 title = "Why Has the Natural Rate of Unemployment Increased over Time?",
 author = "Chinhui Juhn and Kevin M. Murphy and Robert H. Topel",
 institution = "National Bureau of Economic Research",
 type = "Working Paper",
 series = "Reprint Series",
 number = "1694",
 year = "1992",
 month = "February",
 URL = "http://www.nber.org/papers/r1694",
 abstract = {},
}