characteristic of the participants. The WHI will generally lack sufficient power to test these subgroup hypotheses unless there are unexpectedly large effects. However, subgroup analyses will be performed to examine:

• The effect of DM plus HRT on breast cancer incidence in women at high and low risk of breast cancer.

• The effect of DM plus HRT on the incidence of coronary and other cardiovascular disease and breast cancer, compared with each therapy alone.

• The effect of HRT on the incidence of coronary and other cardiovascular disease in women with and without cardiovascular disease at baseline.

• The effect of HRT on the incidence of coronary and other cardiovascular disease and breast cancer in obese and lean women.

• The effect of ERT on the incidence of coronary and other cardiovascular disease among women with and without a uterus.

• The effect of HRT plus CaD on fracture rates, compared with each therapy alone.

• The effect of CaD on fractures and colorectal cancer in women with lower and higher intakes of dietary calcium.

• The effect of DM, HRT, and CaD in subgroups of women defined by age and race/ethnicity.

The CT will also offer an opportunity to examine a number of other pertinent factors, including the following:

• The effect of each treatment on perceived quality of life, on combined primary and secondary endpoints, and on total mortality.

• The effects of DM and HRT on lipids, lipoproteins, clotting factors, blood pressure, body mass index, waist-to-hip ratio, and blood glucose.

• Trends in the magnitude of DM, HRT, and CaD effects across age categories and across values of other participant characteristics.

• The relationship to clinical outcomes of (a) baseline biochemical and physical variables, (b) changes in those variables induced by treatment, and (c) adherence.

• The effect of the treatments on a variety of subsidiary endpoints, such as other cancers (ovarian, endometrial), diabetes mellitus, and other age-related outcomes.