Scarpitti, Frank R., author
Holt, Rinehart and Winston, 1974
Buku Teks
Mayo, Elton, author
Division of Research, Graduate School of Business Administration, Harvard University, 1946
Buku Teks
American Psychological Association, 2004
Buku Teks
Kornblum, William, author
Prentice-Hall, 1992
Buku Teks
Palen, J. John, author
McGraw-Hill, 1979
Buku Teks