Menstrual synchrony
Strassmann argued menstrual synchrony defined as menstruation overlap should be quite common. For example, the expected difference by chance between two women with 28-day cycles—which is approximately the average length of menstrual cycles of women at the age —is 7 days. Considering that the mean duration of menses is 5 days and the range is 2 to 7 days, the probability of menstruation overlap by chance should be high.
Menstrual cycle
Preferences for voice pitch change across the cycle. When seeking a short term mating partner, women may prefer a male with a low voice pitch, particularly during the fertile phase. During the late follicular phase, it is common for women demonstrate a preference for mates with a masculine, deep voice. Research has also been conducted on the attractiveness of the female voice throughout the cycle. During their most fertile phase of the menstrual cycle, there is some evidence that female voices are rated as significantly more attractive. This effect is not found with women on the birth control pill.