Schwandt, Thomas A.
Sage, 2001
Buku Referensi
Creswell, John W.
Sage, 1998
Buku Teks SO
Creswell, John W.
SAGE Publications, 2018
Buku Teks SO
Glaser, Barney G.
Aldine, 1967
Buku Teks SO
Ragin, Charles C.
University of California Press, 1987
Buku Teks SO