Tilley, Andrew J.
Pineapple Press, 2003
Buku Teks
Paul M. Camic, Jean E. Rhodes, Lucy Yardley
APA, 2007
Buku Teks
Gomm, Roger
Palgrave-Macmillan, 2004
Buku Teks SO
Zechmeister, Eugene B.
McGraw-Hill, 1992
Buku Teks
McInerney, Dennis M.
Sage Publication, 2001
Buku Teks