1. American Chronology (2019).
http://www.usahistory.info/timeline/
2. American Pain Society (2019).
http://americanpainsociety.org/
3. Americans with Disabilities Act (n.d.).
https://www.ada.gov/
4. Centers for Disease Control and Prevention (2016).
https://www.cdc.gov/media/releases/2016/p0804-ethnic-groups-smoking.html
5. Centers for Disease Control and Prevention (2017).
https://www.cdc.gov/hiv/statistics/overview/ataglance.html