Locke, Lawrence F.
Sage, 1987
Buku Referensi
Locke, Lawrence F.
Sage, 2014
Buku Teks
Denscombe, Martyn
Open University Press, 2012
Buku Teks
Jähne, Johannes
Edition Leipzic, 1964
Buku Teks
Thomas, R. Murray (Robert Murray), 1921-
Corwin Press, 2008
Buku Teks