@inbook{NBERc7600,
 Crossref = "NBERunkn57-3",
 title = "Problems of Assessing Regional Economic Progress",
 author = "Harvey S. Perloff",
 BookTitle = "Regional Income",
 Publisher = "NBER",
 pages = "35-68",
 year = "1957",
 URL = "http://www.nber.org/chapters/c7600",
}
@book{NBERunkn57-3,
 title = "Regional Income",
 author = "Conference in Research in Income and Wealth",
 institution = "National Bureau of Economic Research",
 type = "Book",
 publisher = "NBER",
 year = "1957",
 URL = "http://www.nber.org/books/unkn57-3",
}