1. Centers for Disease Control and Prevention. National Center for Chronic Disease Prevention and Health Promotion, Office on Smoking and Health, Department of Heath and Human Services. Smoking and Tobacco Use - Fact Sheet: Health Effects of Cigarette Smoking 2008 http://www.cdc.gov/tobacco/data_statistics/fact_sheets/health_effects/effects_cig_smoking/
2. Centers for Disease Control and Prevention Tobacco Use in the United States http://www.cdc.gov/tobacco/overview/tobus_us.htm 2003