Johnson, Alvin S., author
Hearh & Co., 1911
Buku Teks
Hicks, John R., author
The Clarendon Press, 1952
Buku Teks
Becker, William E., author
Prentice-Hall, 1971
Buku Teks
Hicks, John R., author
Oxford University Press, 1975
Buku Teks
Robinson, Marshall A., author
Brookings Institution, 1962
Buku Teks