1. United States Census Bureau: American FactFinder [US Census Bureau]. 2013. Available at: www.census.gov. Accessed January 2, 2013.
2. The next four decades - the older population in the United States: 2010 to 2050;Vincent,2010
3. World health statistics 2012,2012
4. Population aging: a comparison among industrialized countries;Anderson;Health Aff,2000
5. The global burden of disease 2004 update,2004