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Bad Moon Rising

In Dispute: Women in close proximity synchronise periods

A 1971 study found that women in the same dormitory tended to synchronize their periods. Subsequent studies have weakly supported the observation, though not everyone finds an effect, and even positive studies don't find an absolute effect; it's only a tendency, not a powerful force. Original reference: Nature 1971 Jan 22;229(5282):244-5; Subsequent references: Annu Rev Sex Res 1998;9:77-95; Physiol Behav 1995 Nov;58(5):883-9; Psychoneuroendocrinology 1991;16(4):353-9