Artikel Jurnal
Nicolas A. Valcik, editor
Routledge, Taylor & Francis Group, 2020
Buku Teks
Richards, Larry E., author
McGraw-Hill , 1983
Buku Teks
Parks, Walter, author
UnknownTruths.com, 2004
Buku Teks
Armstrong, Kenneth A., author
Cambridge University Press, 2017
eBooks