1. World Health Organization Family Planning. Fact sheet no. 351, updated May 2013 http://www.who.int//mediacentre/factsheets/fs351/en/
2. United Nations Population Division Estimates and Projections of Family Planning Indicators 2014 http://www.un.org/en/development/desa/population/theme/family-planning/cp_model.shtml
3. United Nations Trends in contraceptive methods used worldwide. Population facts No. 2013/9 http://www.un.org/en/development/desa/population/publications/pdf/popfacts/popfacts_2013-9.pdf
4. Trends in contraceptive use in the United States: 1982-1995;Piccinino;Fam Plann Perspect,1998
5. Male and female sterilization;Melville;Obstet Gynaecol Reprod Med,2008