White, Rodney R.
John Wiley & Sons, 1994
Buku Teks
Centre for research of human resources and the nvironment University of Indonesia, 1991
Buku Referensi
Leitmann, Josef
McGraw-Hill, 1999
Buku Teks
Artikel Jurnal
Ministry of Foreign Affairs, Japan, 1974
Buku Teks