1. World Health Organization website.
http://www.who.int
. Accessed 12 Mar 2015.
2. “Definition of an older or elderly person.” World Health Organization.
http://www.who.int/healthinfo/survey/ageingdefnolder/en/
. Accessed 12 Mar 2015.
3. US Department of Health and Human Services. Aging statistics.
http://www.aoa.acl.gov/Aging_Statistics/index.aspx
. Accessed 12 Mar 2015.
4. U.S. Census Bureau. International database.
http://www.census.gov/population/www/projections/natdet-D1A.html
. Accessed 12 Mar 2015.
5. Kinsella K, Velkoff V. U.S. Census Bureau. An Aging World: 2001. Washington, DC: U.S. Government Printing Office, 2001; series P95/01-1.