Player, Mack A., author
West Publishing, 1981
Buku Referensi
Rodgers, William H., author
St. Paul Minn, 1977
Buku Teks
Rodgers, William H., author
West Publishing, 1994
Buku Teks
Kubasek, Nancy K., author
Pearson - Prentice Hall, 2005
Buku Teks
Gaba, Jeffrey M., author
United States of America, 1994
Buku Teks