Alexander-Frutschi, author
Stanford Research Institute, 1963
Buku Teks
Slate, Floyd O.
Cornell University, 1974
Buku Referensi
edited by David Eade; John Hodgson
North Holland Publishing Company, 1981
Buku Teks
Nafziger, E. Wayne, author
Cambridge University Press, 2006
Buku Teks
Todaro, Michael P., author
Longman, 1997
Buku Teks