The assessment of menstrual synchrony: comment on Weller and Weller (1997)

A. Weller and L. Weller (1997) claimed to report "the definitive study of menstrual synchrony" (p. 148). To allow for cycle variability, they used the following criterion for synchrony: It occurred in 2 out of 3 months. The underlying assumption of the state of menstrual synchrony is that cycle length variability is minimal. The present article uses a random selection of cycle lengths from a distribution described by R. F. Vollman (1977) to illustrate how variable cycle lengths cause a fluctuation from synchrony to a synchrony. A. Weller and L. Weller's (1997) study is not, therefore, conclusive, and future studies of menstrual synchrony should include an assessment of cycle variability as well as onset difference.