@inbook{NBERc9096,
 Crossref = "NBERsmit77-1",
 title = "The Market for Optometric Services in the United States in the 1960s",
 author = "Douglas Coate",
 BookTitle = "Explorations in Economic Research, Volume 4, number 2",
 Publisher = "NBER",
 pages = "99-111",
 year = "1977",
 month = "June",
 URL = "http://www.nber.org/chapters/c9096",
}
@book{NBERsmit77-1,
 title = "Explorations in Economic Research, Volume 4, number 2",
 author = "NBER",
 institution = "National Bureau of Economic Research",
 type = "Book",
 publisher = "NBER",
 year = "1977",
 URL = "http://www.nber.org/books/smit77-1",
}