An Event History Analysis of Age at Last Menstrual Period: Correlates of Natural and Surgical Menopause among Midlife Wisconsin Women

Shinberg, Diane
Working paper no. 1995-18


The aging of the U.S. population coupled with heightened consumerism among those using the health care system have increased public and research interest in menopause. Despite these trends, we know little about the process of menstrual cessation. This paper reviews previous claims regarding secular trends in menopausal age by considering how menstrual cessations differ by type: (1) that due to surgical intervention such as hysterectomy, and (2) that due to “natural” (non-surgical) menopause.

Kaufert recommends that the experience of surgically-induced menopause (through the removal of the uterus and/or ovaries) be excluded from analyses of naturally-occurring menopause. However, analyses of menopause that exclude hysterectomized women are flawed, because such women constitute a high proportion of American women at mid-life. In 1992, 580,000 women had their uteri surgically removed, and cumulatively more than one-third of U.S. women will undergo this procedure by age sixty.

Competing risk survival analysis techniques are applied to model the shape of the underlying hazards for reproductive organ surgery versus “natural” menopause among 3506 mid-life women from the Wisconsin Longitudinal Study. Actuarial life table estimates and non-parametric Kaplan-Meier estimates are used as exploratory techniques. Weibull models are used to evaluate effects of a variety of possible correlates (including education, mental ability, occupation, family background, fertility experience, smoking behavior and hormone therapy). While socioeconomic parameters do contribute to observed differences in age at menstrual cessation, these factors operate through more proximate health-related behaviors (such as smoking in the case of natural menopause and fertility for surgical menopause).