| Abstract: | The length of the menstrual and ovulatory cycle in women is notoriously variable. The frequency distribution of menstrual intervals for women and girls are both positively skewed. Researchers studying the rhythm or similar methods of birth control typically model the system as being symmetric, which introduces an error into the model (a drastic one for the woman who may fall into the area ignored). This research was an attempt to break down the female reproductive system into its controlling components, and mathematically describe the distribution of menstrual intervals. The modeling of these components was based on the work of Sharp et. al. (1977). It is shown in this analysis that the distribution of human menstrual intervals can be based upon the following two assumptions. 1) The interval length is dependant on the normally distributed development rate of the follicle/corpus luteum. From this, the positive skew in menstrual intervals follows mathematically. 2) The actual distribution of menstrual intervals can be described by a combination of development rates each representing a subgroup of the population by "cycle age" (number of cycles since menarche-first menstruation). The distribution model developed agrees with the observed data for normal pubertal girls and for normal women. |
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