Brookings institution, 1949
Buku Teks
Pratt, Julius W.
Prentice-Hall, 1965
Buku Teks
edited by Robert W. Tucker, Charles B. Keely, and Linda Wrigley
Westview Press, 1990
Buku Teks
Hartmann, Frederick H.
Macmillan, 1985
Buku Teks
Brokings Institution, 1950
Buku Teks