@inbook{NBERc10130,
 Crossref = "NBERhult01-1",
 title = "Sources of Productivity Growth in the American Coal Industry 1972–95 ",
 author = "Denny Ellerman and Thomas Stoker and Ernst R. Berndt",
 BookTitle = "New Developments in Productivity Analysis",
 Publisher = "University of Chicago Press",
 pages = "373-418",
 year = "2001",
 month = "January",
 URL = "http://www.nber.org/chapters/c10130",
}
@book{NBERhult01-1,
 title = "New Developments in Productivity Analysis",
 author = "Charles R. Hulten and Edwin R. Dean and Michael J. Harper",
 institution = "National Bureau of Economic Research",
 type = "Book",
 publisher = "University of Chicago Press",
 year = "2001",
 URL = "http://www.nber.org/books/hult01-1",
}