Covey, Stephen R., author
Simon & Schuster, 1990
Buku Teks
Covey, Stephen R., author
Simon & Schuster, 1991
Buku Teks
Fakultas Psikologi Universitas Indonesia, 2003
UI - Skripsi (Membership)
Covey, Stephen R., author
Binarupa Aksara, 1997
Buku Teks
Koestenbaum, Peter
Jossey-Bass Publishers, 1991
Buku Teks