This theory was based on the belief that women who live together will start their period within 2-4 days of each other within 4-6 months. This statement was thought to be true after Martha McClintock (a graduate student at the time) published her research findings in “Nature” magazine back in 1971. Ms. McClintock’s research was based on observations she made of 135 college students at Wellesley College. Since that time, researchers have tried to duplicate this model, observing larger numbers of women; however, the findings are inconsistent and do not prove the theory. So, if you notice that all the women in your family or your roommates have periods that start within a couple of days of each other, it’s probably by chance.