McDowell, Ian
Oxford University Press, 1996
Buku Teks
Peterson, Robert A.
Sage Publications, Inc., 2000
Buku Teks
Foddy, William
Cambridge University Press, 1993
Buku Teks
Streiner, David L.
Oxford University Press, 2015
Buku Teks
Bradburn, Norman
Jossey-Bass, 2004
Buku Teks