1. Wendell Cox Consultancy/Demographia U.S. population from 1900 (statistics from U.S. Census Bureau) www.demographia.com/db-uspop1900.htm
2. Rosenberg M Current U.S.A. population http://geography.about.com/od/obtainpopulationdata/a/uspopulation.htm
3. U.S. Census Bureau Aging boomers will increase dependency ratio, census bureau projects: older American population to become more diverse www.census.gov/newsroom/releases/archives/aging_population/cb10-72.html
4. General dentists and special needs patients: does dental education matter?;Dao;J Dent Educ,2005