Ward, Ralph D.
John Wiley & Sons, 1997
Buku Teks SO
Puckey, Walter, Sir
Hutchinson of London, 1969
Buku Referensi
Domhoff, G. William
McGraw-Hill, Higher Education, 2010
Buku Teks SO
Vance, Stanley C.
McGraw-Hill , 1983
Buku Teks SO
Tedford, Thomas L.
McGraw-Hill, 1991
Buku Teks SO