Dimock, Marshall Edward
Henry Holt, 1953
Buku Teks
Isaacs, Asher, 1902-1963
Van Nostrand , 1964
Buku Teks SO
Lyon, Leverett S.
The Brookings Institution, 1940
Buku Teks
Gujarati, Damodar N.
McGraw-Hill, 1984
Buku Teks SO
Griffin, Ricky W.
Prentice-Hall, 1993
Buku Teks