Morehead, Joe
Libraries Unlimited, 1978
Buku Teks
Schmeckebier, Laurence F.
The Brookings Institution , 1961
Buku Teks
Maxwell, James A.
Harvard University Press, 1946
Buku Teks
Boyd, Anne Morris
H.W. Wilson, 1949
Buku Teks
Kling, Robert E.
Praeger , 1970
Buku Teks