[1] “Historic Estimates of World Population,” U.S. Census Bureau, http://www.census.gov/ipc/www/worldhis.html .
[2] “World POPClock Projection: Monthly World Population Figures,” U.S. Census Bureau, http://www.census.gov/ipc/www/popclockworld.html .
[3] U.N. Population Division, Population Division of the Department of Economic and Social Affairs of the U.N. Secretariat, World Population Prospects: The 2008 Revision, http://www.un.org/esa/population/publications/wpp2008/wpp2008_text_tables.pdf.
[4] U.N. Population Division, Population Division of the Department of Economic and Social Affairs of the U.N. Secretariat, World Population Prospects: The 2008 Revision.
[5] As set out in U.N. General Assembly resolutions 59/209, 59/210 and 60/33 in 2007.  Of the forty-nine countries, thirty-three are in Africa, ten in Asia, one in Latin America and the Caribbean, and five in Oceania.  See “Definition of major areas and regions," World Population Prospects: The 2008 Revision.
[6] Media Eghbal, “Special Report: Global Youth Populations,” Euromonitor International, November 21, 2008, http://www.euromonitor.com/Special_Report_Global_youth_populations .
[7] U.N. Population Division, Population Division of the Department of Economic and Social Affairs of the U.N. Secretariat, World Population Prospects: The 2008 Revision. http://esa.un.org/unpp/ .
[8] Population Division of the Department of Economic and Social Affairs of the United Nations Secretariat, World Population Prospects: The 2006 Revision and World Urbanization Prospects: The 2007 Revision, and World Urbanization Prospects: The 2008 Revision. 
[9] Population Division of the Department of Economic and Social Affairs of the United Nations Secretariat, World Population Prospects: The 2006 Revision and World Urbanization Prospects: The 2007 Revision, and World Urbanization Prospects: The 2008 Revision.
[10] UNFPA, Supporting Adolescents and Youth. http://www.unfpa.org/adolescents/overview.htm .
[11] UNFPA, State of the World Populations 2007: Unleashing the Potential for Urban Growth. http://www.unfpa.org/swp/2007/english/introduction.html .
[12] Population Reference Bureau, 2007 World Population Data Sheet. [cited 13 February, 2009],  p.7, http://www.prb.org/pdf07/07WPDS_Eng.pdf. 
[13] Allianz Knowledge Partnership, The Future is Urban. 2007 [cited 13 February 2009]. http://knowledge.allianz.com/en/globalissues/demographic_change/urbanization/urbanization_cities.html.
[14] UNFPA, State of the World Populations 2007: Unleashing the Potential for Urban Growth. [cited 28 February 2008], http://www.unfpa.org/swp/2007/english/chapter_1/index.html .
[15] U.N. Population Division, Population Division of the Department of Economic and Social Affairs of the U.N. Secretariat, World Population Prospects: The 2008 Revision.
[16] UN Department of Economic and Social Affairs Population Division, World Population Prospect, the 2004 Revision: Highlights (New York: United Nations, 2004), p. 9. http://www.un.org/esa/population/publications/WPP2004/wpp2004.htm.
[17] Population Reference Bureau, "World Data: Population Trends," http://www.prb.org/Datafinder/Topic/List.aspx?category=10.
[18] “Pakistan’s population to double by 2050: UN,” Asian Tribune, 29 Jul 2009, http://asiantribune.com/07/29/pakistan%E2%80%99s-population-to-double-by-2050-un/ .