Synchronicity

Is it really true that women who “live together, menstruate together”?

Do women's menstrual cycles really align when they live together? (Photograph: Dan Burn-forti/Getty Images)

The commonly accepted “fact” that women who live together will have their menstrual cycles “synchronize” with each other, a concept based almost entirely on one 1971 study, has been debunked by modern studies, according to researchers.

The idea that women who “live together, menstruate together” had proliferated in scientic fields, and popular culture, ever since Martha McClintock, a psychologist from Harvard University, published a study on the cycles of 135 female undergraduates living together in a Harvard dormitory in 1971. McClintock found that roommates and close friends saw the average number of days between the starts of their periods fall from eight or nine days down to five. A control group, meanwhile, saw the average number of days between the start of their periods remain at 10 days apart. By 1999, the idea had become pervasive in popular culture: One study at the time found that 80 percent of women believed in synchronicity — 70 percent describing the experience as a pleasant one.

In later years, however, McClintock’s work has been taken to task for statistical errors that led the apparent synchronicity to be overstated. And while many studies have attempted to replicate McClintock’s findings, the majority have found no evidence of synchronicity whatsoever. One study of Dogon women in west Africa found no synchronicity over 763 days after women were segregated into menstrual huts. A study of 186 women in China also found no synchronicity after a year, as did another study of 26 lesbian couples. The natural variability of cycles, researchers suggest, may have given a false impression of synchronicity in previous studies. The synchronized period, it would appear, was nothing more than a modern myth.

Read the full story at The Guardian.

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