A study conducted in 40 US clinical centers beginning in 1993. Enrolled were 10,739 postmenopausal women, aged 50-79 years, with prior hysterectomy, including 23% of minority race/ethnicity.

Women were randomly assigned to receive either 0.625 mg/d of conjugated equine estrogen (CEE) or placebo.

What is the study design?
a) Cross-sectional
b) Cohort
c) Randomized clinical trial
d) Ecological