Hamilton, Robert W., author
West Publishing, 1992
Buku Teks
Donaldson, Thomas
Prentice-Hall, 1981
Buku Teks
Henn, Harry, Alexander, John R
St.Paul,Minn : West publishing Co, 1983,
Buku Referensi
Gregory, William A., author
Anderson Publishing, 1999
Buku Teks
LaPalombara, Joseph, author
Conference Board, 1977
Buku Teks