Dimock, Marshall Edward
Walker, 1970
Buku Teks
Griffiths, Richard, 1935-
Constable, 1994
Buku Teks
Banfield, Edward C.
Free Press, 1951
Buku Teks
Gujarati, Damodar N.
McGraw-Hill, 1984
Buku Teks
Hall, Ford P.
McGraw-Hill Book Company,Inc., 1949
Buku Teks