El 19 de marzo y el 2 de mayo
The 1999 CIA World Factbook
The 1998 CIA World Factbook
The 1997 CIA World Factbook
The 1996 CIA World Factbook
1995 United States Congressional Address Book
The 1995 CIA World Factbook
The 1994 CIA World Factbook
The 1993 CIA World Factbook
The 1992 CIA World Factbook
The 1991 CIA World Factbook
The 1990 United States Census [2nd]
The 1990 United States Census
The 1990 CIA World Factbook
1931: A Glance at the Twentieth Century
The 1926 Tatler