Hamburg, Morris
Harcourt Brace Javanovich , 1974
Buku Teks
Michael S. Lewis-Beck, editor
Sage Publications, 1993
Buku Referensi
Moore, David S., author
W.H. Freeman, 2000
Buku Teks
Kaplan, Robert M., author
Allyn and Bacon , 1987
Buku Teks
Hoel, Paul Gerhard, 1905-, author
Wiley, 1982
Buku Teks