In menstrual cycle stage a confounder in population-based psychiatric research?

It has been suggested that a failure to control for point in the menstrual cycle can lead to biased results in assessing psychiatric symptoms among women since state affects associated with premenstrual symptoms may lead to unreliability of symptom reporting as well as an artificial elevation of symptom ratings. We examine these hypotheses and the extent to which they can account for gender differences in symptom scale scores of demoralization and enervation.

The data are derived from an epidemiological study of Jews born in Israel between 1949 and 1958. The symptom scale scores of 2265 men and 1769 women (368 premenstrual, 458 menstruation and 943 postmenstrual) were compared regarding reliability, homogeneity and mean score.

There were no differences among the menstrual groups, or between the men and women, in reliability of their responses as measured by the alpha coefficient and the coefficient of variation. There were no significant differences among the female groups on mean symptom scale score. The mean scale scores for each female group were significantly higher than the mean scores for men.

Our results suggest that menstrual cycle stage does not influence the reliability of reporting, the variability of response or mean symptom levels. However, our conclusions may not apply to studies of drug effects or clinical studies of premenstrual dysphoria.