Correlates of prospectively defined premenstrual syndrome were
investigated in 50 women who visited a premenstrual syndrome clinic. To
assess premenstrual symptom change relative to daily change, the author
used effect size, the difference in mood ratings between the post- and
premenstrual phases divided by the standard deviation of the entire cycle.
Only 12 women had an effect size greater than or equal to 1.0 in two
cycles. The probability of having premenstrual syndrome was positively
related to working outside the home and negatively related to age. The
results underscore the need to use prospective diagnostic criteria in
research on premenstrual syndrome.