Rudestam, Kjell Erik
Sage Publications, 1992
Buku Teks
Mauch, James E.
Marcel Dekker, Inc., 1993
Buku Teks
Thomas, Robert Murray, 1921-
Corwin Press, 2008
Buku Teks
Thomas, Robert Murray, 1921-
Bergin & Garvey, 2000
Buku Teks
Garson, G. David
Marcel Dekker, 2002
Buku Referensi