1. Sharing responsibility: women, society and abortion worldwide;The Alan Guttmacher Institute,1999
2. Disparities in rates of unintended pregnancy in the United States, 1994 and 2001;Finer;Perspect Sex Reprod Health,2006
3. Improving contraceptive use in the United States;Frost,2008
4. Facts on contraceptive use;Guttmacher Institute,2008