April 19, 2017 report
Study suggests menstrual-cycle syncing by women does not really happen
It is a commonly held notion that women who live or work together, or just spend a lot of time together, find their menstrual cycles syncing. There was even a study done in 1971 by Harvard researcher Martha McClintock tracking the menstrual cycles of female colleges students sharing a dorm. But, as the researchers with this new effort note, no other studies have found it to be true, and McClintock's work has been discredited. But sill the myth persists. To perhaps put an end to the debate, the researchers conducted a test trial with women who use the Clue app—1500 women responded to their request for assistance in a trial and out of those, 360 pairs of women were selected for inclusion. Each were in a close relationship with another woman over an extended period of time. Because the app helps women track and share their period information, the data was already available; all that was needed was for the users to share it with the researchers.
The researchers looked back three menstrual cycles for each of the pairs to see if any alignment was occurring and report that 273 of them actually had cycles that diverged—just 79 were seen to converge. They note that women who were living together were no more aligned than the other pairs. This, they insist, is further proof that the entire idea is a myth with no basis in reality.
Regarding why so many women believe the myth, the researchers suggest it has to do with chance and emotion—cycles last on average 28 days, which means a pair could, at most, be out of sync just 14 days. Simple math shows they would be out of sync on average just seven days, which could lead to a misperception of syncing, especially considering that the myth is so prevalent.
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