Ripley, Randall B.
The Dorsey Press, 1980
Buku Teks
by James E. Anderson; David Brady; Charles Bullock III; Joseph stewart, JR
Brooks/Cole; cengage learning, 1984
Buku Teks
Purdy, Harry Leslie, author
Prentice-Hall, 1942
Buku Teks
Edited by B. Guy Peters, Jon Pierre
Sage, 2015
Buku Referensi
Routledge, 2013
Buku Teks