Erickson, Bonnie H., author
Open University Press, 1977
Buku Teks
Thompson, Bruce, author
APA, 2004
Buku Teks
Stebbins, Robert A., author
Sage, 2001
Buku Teks
Blackman, Sheldon, author
John Wiley & Sons, 1971
Buku Teks
Tukey, John Wilder, 1915-, author
Addison-Wesley, 1977
Buku Teks