Haviland, H. Field
The Brooking Institution, 1960
Buku Teks
Keiser, Norman F.
John Wiley & Sons, 1964
Buku Teks
edited by Warren L. Smith and Ronald L. Teigen
Ill R. D. Irwin , 1970
Buku Teks
Colm, Gerhard
Brookings Institution , 1969
Buku Teks
Prentice-Hall, 1960
Buku Teks