Psacharopoulos, George, author
World Bank, 1993
Buku Teks
Munk, Arthur W.
Abingdon Press, 1965
Buku Teks
Falmer Press, 1998
Buku Teks
Smith, L. Glenn, author
Allyn and Bacon, 1973
Buku Teks
Williams, Gareth, author
PSI, [date of publication not identified]
Buku Teks