Banco Mundial, 2007
Buku Teks
Kitchen, Richard L.
John Wiley & Sons, 1986
Buku Teks SO
edited by Stephan Haggard, Chung H. Lee and Sylvia Maxfield
Cornell University Press, 1993
Buku Teks SO
Matherson, Ross
John Wiley & Sons, 1978
Buku Teks SO
editor, Walter B. Stohr, D.R. Fraser Taylor
John Wiley & Sons, 1981
Buku Teks SO