Effectiveness of the natural family planning method by considering unobserved heterogeneity

The natural family planner methods are becoming widespread to consider the fertile or infertile period of a woman. The post ovulation phase of the woman’s menstrual cycle is considered as an important period of time due to the fact that the ovum survive maximum two days after the ovulation. However to determine such period of time is a difficult as the ovulation is not really linked to the overall length of the cycle. By relying on historical data we show some evidences by comparing the calendar method and the Ogino-Knaus method. We propose a suitable statistical model which uses the basal body temperature and the characteristics of vulval secretions in order to capture unobserved heterogeneity in the population of interest.