@inbook{NBERc9685,
 Crossref = "NBERenge86-1",
 title = "Rudimentary Contraceptive Methods and the American Transition to Marital Fertility Control, 1855-1915",
 author = "Paul David and Warren Sanderson",
 BookTitle = "Long-Term Factors in American Economic Growth",
 Publisher = "University of Chicago Press",
 pages = "307-390",
 year = "1986",
 URL = "http://www.nber.org/chapters/c9685",
}
@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",
}