Hammersley, Martyn, author
Paul Chapman Publishing, 2002
Buku Teks
American Psychological Association, {s.a}
Majalah, Jurnal, Buletin
Hesse-Biber, Sharlene Nagy, author
Sage, 2007
Buku Teks
Phillips, Don T., author
John Wiley & Sons, 1976
Buku Teks
Ravindran, A., author
John Wiley & Sons, 1987
Buku Teks