Stein, Lincoln D., author
Wiley, 1998
Buku Teks
Langer, Maria, author
Osborne/McGraw-Hill, 1999
Buku Referensi
Central Statistical Office
Her Majesty`s Stationery Office, 1986
Buku Referensi
Oehler, Karsten, author
McGraw-Hill, 2012
Buku Teks
McCracken, Daniel D., author
John Wiley & Sons, 1974
Buku Referensi