Watson, George, author
Longman, 1987
Buku Teks
Rudestam, Kjell Erik
Sage Publications, 1992
Buku Teks
Mauch, James E.
Marcel Dekker, Inc., 1993
Buku Teks
Thomas, R. Murray (Robert Murray), 1921-, author
Corwin Press, 2008
Buku Teks
Garson, G. David, author
Marcel Dekker, 2002
Buku Referensi