editor, Owen D.W. Hargie
Routledge, 1997
Buku Referensi
Northouse, Peter G., author
Prentice-Hall, 1985
Buku Referensi
Guthrie, L.O., author
Macmillan, 1956
Buku Teks
Rawlins, Karen
MacMillan Press , 1993
Buku Teks
Pender, Harold, author
John Wiley & Sons, 1950
Buku Referensi