Phillips, Nelson, author
Sage, 2002
Buku Teks
edited by Garth J.O. Fletcher and Margaret S. Clark
Blackwell, 2003
Buku Teks
Titmuss, Richard M
Longmans Green and Co, 1950
Buku Teks
Schey, John A., author
McGraw-Hill, 2000
Buku Teks
Iosifescu, Marius, author
John Wiley & Sons, 1980
Buku Teks