@inbook{NBERc7605,
 Crossref = "NBERunkn57-3",
 title = "City Size and Income, 1949",
 author = "Edwin Mansfield",
 BookTitle = "Regional Income",
 Publisher = "NBER",
 pages = "271-318",
 year = "1957",
 URL = "http://www.nber.org/chapters/c7605",
}
@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",
}