Rudestam, Kjell Erik
Sage Publications, 1992
Buku Teks
Watson, George, author
Longman, 1987
Buku Teks
Osbeck, Mark K., author
Thomson/West, 2010
Buku Teks
Allard, Patsy Bailey, author
AMA Membership Publications Division, American Management Associations, 1983
Buku Referensi
Mauch, James E.
Marcel Dekker, Inc., 1993
Buku Teks