United Nations Population Fund. (1999). The State of world population 1999: 6billion : a time for choices. UNFPA.
Citazione stile Chigago Style (17a edizione)United Nations Population Fund. The State of World Population 1999: 6billion : A Time for Choices. New York: UNFPA, 1999.
Citatione MLA (8a ed.)United Nations Population Fund. The State of World Population 1999: 6billion : A Time for Choices. UNFPA, 1999.
Attenzione: Queste citazioni potrebbero non essere precise al 100%.