Rapport, Nigel, author
Routledge, 2000
Buku Teks
Crapo, Richley H., author
McGraw-Hill, 2002
Buku Teks
Schusky, Ernest l.
Holt Rinehart and Winston, 1975
Buku Teks
Ember, Carol R., author
Prentice-Hall, 1988
Buku Teks
Kottak, Conrad Phillip, author
McGraw-Hill, 2012
Buku Teks