Trussell, James (2011). "Contraceptive efficacy"(PDF). Dalam Hatcher, Robert A.; Trussell, James; Nelson, Anita L.; Cates, Willard Jr.; Kowal, Deborah; Policar, Michael S. (penyunting). Contraceptive technology (ed.20th revised). New York: Ardent Media. m/s.779–863. ISBN978-1-59708-004-0. ISSN0091-9721. OCLC781956734. Diarkibkan(PDF) daripada yang asal pada 2013-11-12.
Trussell, James (2011). "Contraceptive efficacy"(PDF). Dalam Hatcher, Robert A.; Trussell, James; Nelson, Anita L.; Cates, Willard Jr.; Kowal, Deborah; Policar, Michael S. (penyunting). Contraceptive technology (ed.20th revised). New York: Ardent Media. m/s.779–863. ISBN978-1-59708-004-0. ISSN0091-9721. OCLC781956734. Diarkibkan(PDF) daripada yang asal pada 2013-11-12.
Trussell, James (2011). "Contraceptive efficacy"(PDF). Dalam Hatcher, Robert A.; Trussell, James; Nelson, Anita L.; Cates, Willard Jr.; Kowal, Deborah; Policar, Michael S. (penyunting). Contraceptive technology (ed.20th revised). New York: Ardent Media. m/s.779–863. ISBN978-1-59708-004-0. ISSN0091-9721. OCLC781956734. Diarkibkan(PDF) daripada yang asal pada 2013-11-12.