DuaneM., MotleyR., and ManhartM.. 2013. Physicians need more education about natural family planning. Letter to the editor. American Family Physician88, no. 3: 158–9.
2.
ManhartMichael D., DuaneM., LindA. L., SinaiI., and Golden-TevaldJ.. 2013. Fertility awareness-based methods of family planning: A review of effectiveness for avoiding pregnancy using SORT. Osteopathic Family Physician5: 2–8.
3.
Mulcaire-JonesGeorge, FehringRichard J., BradshawMegan, BrowerKaren, LubegaGonzaga, and LubegaPaskazia. 2016. Couple Beads: An integrated method of natural family planning. Linacre Quarterly83: 69–82.
4.
TrussellJ., and Grummer-StrawnL.. 1991. Further analysis of contraceptive failure of the ovulation method. American Journal of Obstetrics and Gynecology165: 2054–9.