Riffenburgh, Robert H., author
lsevier Science, 2012
Buku Teks SO
edited by Michael S. Lewis-Beck
Sage, 1993
Buku Referensi
Michael S. Lewis-Beck, editor
Sage Publications, 1993
Buku Referensi
Leabo, Dick A., author
Richard D. Irwin, 1968
Buku Teks SO
Levin, Richard I., author
Prentice-Hall, 1998
Buku Teks SO