Indonesia. Badan Pusat Statistik
Badan Pusat Statistik, 2000
Buku Referensi
Stultz, Russell Allen
Prentice-Hall, 1982
Buku Teks
Krieger, Morris
McGraw-Hill, 1985
Buku Teks
McClure, Rhyder, author
Brady, 1990
Buku Teks
Hult, Christine
Wadsworth, 1987
Buku Teks