Slight Increase In Asymmetry

There is the problem of a slight increase in asynchrony (that is, menstrual cycle onset dates are slightly, though progressively, less close together) over the three months of the Bedouin family study, as pointed out by researchers Arden and Dye in 1998. For example, for “roommates-sisters,” synchrony scores are 6.32, 6.24, and 7.40 for months 1, 2, and 3, respectively.

The Bedouin family study assumed that study subjects who had been living together for some time were already in a state of synchrony. This is a departure from the initial McClintock study, which looked at women in the process of becoming synchronized. In their 1996 paper, “Menstrual Variability and the Measurement of Menstrual Synchrony,” Weller and Weller explain:

“Researchers have employed essentially two basic conceptual approaches. The first…focuses on the process of synchronization. According to this approach, synchrony is viewed as a shifting in the timing of menstrual dates occurring during the first months of living together. Women are asked to record their menstrual dates when first starting to live together and then to record all their subsequent dates for the study’s duration. In contrast, the second approach…is not concerned with the process of attaining synchrony, but instead asks whether synchrony has been attained by women who have been living together for a prolonged period of time. If the women are close in their menstrual dates, it is assumed that the synchronization process has occurred.”

Schank points out that the increase in asynchrony also occurs in the study of urban families (L. Weller, Weller, Korsh-Kamin, Ben Shoshan, 1999), and calculated that the probability of these increases in asynchrony occurring by chance in both studies (that is, in a total of eight group synchrony scores over a three-month period) “is only .5⁸ = .004.”

Weller and Weller argue that “there was no significant change in [group] synchrony scores in four out of the five comparisons in the [urban families] study,” and “Therefore Schank’s statement regarding the probability of all eight groups increasing in asynchrony by chance is invalid, for four of the five comparisons (for which tests were performed) were not significant.”

Schank replies: “Weller and Weller (2000) object that not all decreases [in synchrony] were significant. However, this was not the question. I was concerned whether the artifact described by Arden and Dye (1998) occurred in the study, and it does...Why, in all of their studies (in Table 1, Schank, 2001) do scores become more asynchronous by the third cycle where they are supposed to be stably synchronized?”

Click here for a famous example of a seemingly “insignificant” “artifact” playing a decisive role in the acceptance of a scientific theory.

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