Assessment of menstrual synchrony: Reply to comment by Arden and Dye

M. Arden and L. Dye (1998) commented that for the state of menstrual synchrony to reliably persist for a prolonged period, "mean cycle lengths of synchrony partners" should be "approximately equal and vary only minimally around the mean" (p. 323). They implied that this may not have been the case in our sample of Bedouin families (A. Weller & Weller, 1997). A reanalysis of our data shows very low variability of family cycle lengths: Median differences were only 1.4 and 1.3 days. Therefore, Arden and Dye's model (which was based on large variability in cycle lengths) is not appropriate for the Bedouin sample that they criticize, and our reliability criterion of 2 out of 3 months appears to be appropriate. Thus, the Bedouin sample provides conclusive evidence for menstrual synchrony both by the traditional measure of close menstrual onset differences and by Arden and Dye's newly suggested criterion: similar cycle lengths among synchrony partners