With the Billings Ovulation Method of natural family planning, women chart the symptoms of changes of their cervical mucus to determine when they are ovulating. The Ovulation Method is simple to learn, and some studies have shown it to be 98.5% effective. It can be used throughout a woman's child-bearing years. Unlike other methods of natural family planning, a woman need not have regular menstrual cycles to use the Ovulation Method. Usually, volunteer married couples trained in the method teach it; however, the physician's support can greatly increase the competence of these instructors.