Gartside, L. (Leonard), author
Macdonald and Evans, 1982
Buku Teks
Seglin, Jeffrey L., author
Amacom, 1996
Buku Referensi
Merriam-Webster, Inc., 1988
Buku Teks
Merriam-Webster's, Incorporated, 1993
Buku Referensi
Seglin, Jeffrey L., author
[American Management Association, American Management Association], 2002
eBooks