Contraceptive Technology (USA)

http://www.contraceptivetechnology.org/the-book/take-a-peek/contraceptive-efficacy/

 

 

Center for Disease Control and Prevention (USA)

https://www.cdc.gov/reproductivehealth/contraception/index.htm

 

Planned Parenthood (USA)

https://www.plannedparenthood.org/learn/birth-control

 

 

World Health Organization (W.H.O.)

http://www.who.int/mediacentre/factsheets/fs351/en/

 

 

National Health Service (NHS), UK

https://www.nhs.uk/Conditions/contraception-guide/Pages/how-effective-contraception.aspx