Whisler, Thomas L.
Dow Jones-Irwin, 1984
Buku Teks
The Free Press of Glencoe, 1960
Buku Teks
Ward, Ralph D.
John Wiley & Sons, 1997
Buku Teks
Puckey, Walter, Sir, author
Hutchinson of London, 1969
Buku Referensi
Domhoff, G. William, author
McGraw-Hill, Higher Education, 2010
Buku Teks