1. Centers for Disease Control (2008) Cigarette smoking among adults - United States, 2007. Morbidity & Mortality Weekly Report 57, 1221–1226
2. World Health Organization (2009) Tobacco key facts. http://www.who.int/topics/tobacco/facts/en/index.html
3. Actual causes of death in the United States, 2000;Mokdad;JAMA,2004
4. American Cancer Society (2009) Cancer facts & Figures 2009, American Cancer Society
5. Nicotine dependence and genetic variation in the nicotinic receptors;Bierut;Drug Alcohol Depend,2009