Lippincott , 2004
Buku Teks
Gall, Gerald B.
Carswell, 1990
Buku Teks
Buck, A. E., author
Public Administration Service, 1949
Buku Teks
edited by R.C. Bellan, W.H. Pope
McGraw-Hill, 1981
Buku Teks
Friesen, Gerald, author
University of Toronto Press, 1984
Buku Teks