Isaac, Katherine
St. Martin's Press, 1977
Buku Teks
editor by. James A. Maxwell
The Reader's Digest Association Inc., 1984
Buku Referensi
Armstrong, Michael, author
Gramedia, 2003
Buku Teks
edited by Albert Newgardsen
American Management Association, 1959
Buku Teks
Bres, P.
World Health Organization, 1986
Buku Teks