@inbook{NBERc2387,
 Crossref = "NBERuniv60-2",
 title = "An Economic Analysis of Fertility",
 author = "Gary S. Becker and James S. Duesenberry and Bernard Okun",
 pages = "225-256",
 year = "1960",
 URL = "http://www.nber.org/chapters/c2387",
}