Wonderling, David
Open University Press, 2005
Buku Teks
Phelps, Charles E.
Harper Collins, 1992
Buku Teks
Ashmore, Malcolm
Open University Press, 1990
Buku Teks
Donaldson, Cam
Macmillan, 1994
Buku Teks
Cooper, Michael H.
John Wiley & Sons, 1975
Buku Teks