Dalzell, J. Ralph
McGraw-Hill, 1973
Buku Teks
Harker, Ralph J.
John Wiley & Sons, 1983
Buku Teks
Reed, Mortimer P.
Prentice-Hall, 1983
Buku Teks
Davis, Sid, author
American Management Association, 2008
eBooks
Cordiner, Ralph J.
McGraw-Hill Book Company, Inc., 1956
Buku Teks