Eko Budiarto, author
EGC, 2003
Buku Teks
Polgar, Stephen, author
Churchill Livingstone, 1988
Buku Teks
Portney, Leslie Gross, author
Prentice-Hall, 2000
Buku Teks
Rice, Pranee Liamputtong, author
Oxford University Press, 1999
Buku Teks
edited by Janice M. Morse, Janice M. Swanson, and Anton J. Kuzel
Sage, 2000
Buku Teks