Mayhew, Lewis B.
Jossey-Bass, 1973
Buku Teks
Her Majesty's Stationery Office, 1987
Buku Teks
edited by Maria Slowey, David Watson
Open University Press, 2003
Buku Teks
Smith, Huston
Harper & Brothers, 1955
Buku Teks
Burton R. Clark, Guy R. Neave, editors-in-cheif
Pergamon Press, 1992
Buku Referensi