Peters, Robert Henry
The ecological implications of body size / Robert Henry Peters
Cambridge University Press, 1983
 Buku Teks
Phillips, Patricia Pulliam
Return on investment (ROI) basics
American Society for Training & Development, 2005
 eBooks
Pengukuran return on training investment (ROTI)
 Artikel Jurnal
Haugen, Robert A.
Modern investment theory / Robert A. Haugen.
Prentice-Hall, 1990
 Buku Teks
Haugen, Robert A.
Modern investment theory / Robert A. Haugen
Prentice-Hall, 1997
 Buku Teks