1. Martin, J. A., Hamilton, B. E., Sutton, P. D., Ventura, S. J., Menacker, F. & Kirmeyer, S. (2006). Births: Final Data for 2004. National Vital Statistics Reports 55.
2. National Center for Health Statistics (2006). Health, United States, 2006, with Chartbook on Trends in the Health of Americans (http://www.cdc.gov/nchs/data/hus/hus06.pdf#027).
3. He, W., Sengupta, M., Velkoff, V. A. & DeBarros, K. A. (2006). 65+ in the United States: 2005. (U.S. Census Bureau) http://www.census.gov/prod/2006pubs/p23-209.pdf.
4. US Census Bureau (2007). International Database (http://www.census.gov/ipc/www/idb/).
5. United Nations (2001). World Population Prospects: The 2000 Revision (http://www.unece.org/stats/trend/register.htm).