@inbook{NBERc9686,
 Crossref = "NBERenge86-1",
 title = "New Results on the Decline in Household Fertility in the United States from 1750 to 1900",
 author = "Jenny Wahl",
 BookTitle = "Long-Term Factors in American Economic Growth",
 Publisher = "University of Chicago Press",
 pages = "391-438",
 year = "1986",
 URL = "http://www.nber.org/chapters/c9686",
}
@book{NBERenge86-1,
 title = "Long-Term Factors in American Economic Growth",
 author = "Stanley L. Engerman and Robert E. Gallman",
 institution = "National Bureau of Economic Research",
 type = "Book",
 publisher = "University of Chicago Press",
 year = "1986",
 URL = "http://www.nber.org/books/enge86-1",
}