Hall, Ford P
McGraw-Hill, 1949.
Buku Teks
Isaacs, Asher, 1902-1963, author
Van Nostrand , 1964
Buku Teks
Lyon, Leverett S., author
The Brookings Institution, 1940
Buku Teks
Dimock, Marshall Edward, author
Henry Holt , 1953
Buku Teks
Gujarati, Damodar N., author
McGraw-Hill, 1984
Buku Teks