@inbook{NBERc2475,
 Crossref = "NBERunkn60-1",
 title = "Interregional Differences in Per Capita Income, Population, and Total Income, 1840-1950",
 author = "Richard Easterlin",
 BookTitle = "Trends in the American Economy in the Nineteenth Century",
 Publisher = "Princeton University Press",
 pages = "73-140",
 year = "1960",
 URL = "http://www.nber.org/chapters/c2475",
}
@book{NBERunkn60-1,
 title = "Trends in the American Economy in the Nineteenth Century",
 author = "The Conference on Research in Income and Wealth",
 institution = "National Bureau of Economic Research",
 type = "Book",
 publisher = "Princeton University Press",
 year = "1960",
 URL = "http://www.nber.org/books/unkn60-1",
}