, Volume 17, Issue 4, pp 433-447

Women do not synchronize their menstrual cycles

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It is widely believed that women who live together or who are close friends synchronize their menstrual cycles. We reexamined this phenomenon in two ways. First, we collected data on menstrual cycles from 186 Chinese women living in dorms for over a year. We found that women living in groups did not synchronize their cycles. Second, we reviewed the first study reporting menstrual synchrony. We found that group synchrony in that study was at the level of chance. We then show that cycle variability produces convergences and subsequent divergences of cycle onsets and may explain perceptions of synchrony.

This study was supported by the Sichuan Youth Foundation of Science and Technology (Chuan Ke Ji [2001] 2) and NIH Grant No. 5R01MH065555-02. We thank Shuhuan Yang, Xia Xu, Jun Qu, Jing Zhu, Meijia Yu, & Chang Zhou for all their work in collecting the data. Without them, this study could never have been done.
Zheng-Wei Yang is director and professor of the Morphometric Research Laboratory, North Sichuan Medical College, China. His main research interests are in spermatogenesis, morphometry, and stereology.
Jeff Schank is associate professor of psychology at the University of California, Davis. His main research interests are in computational and biorobotic modeling of group behavior and the development of sensorimotor behavior in animals.