How accurate are women's estimates of date of onset of next menses?

Because of individual differences in occurrence of ovulation and patterns of hormonal secretions, one would usually prefer to measure locus in the menstrual cycle using physiological assessment procedures. But such methods are time consuming and costly. When exploring a new domain for possible relations to the menstrual cycle, it would be cost effective to use the simpler procedure of having each women verbally estimate date of onset of next menses. The accuracy of such estimates was studied in two college age samples. Estimated number of days until next onset correlated highly with actual number of days, as verified by follow-up (r = 0.90). As a group, women neither under- nor overestimated number of days. The precision with which these judgments were made was reasonably high. In sum, when a group of women are followed for one cycle, the average accuracy is very high, certainly high enough to support use of such verbal reports for certain scientific purposes.