and Jean Wactawski-Wende10 for the Women’s Health Initiative Investigators

Observational research on postmenopausal hormone therapy suggests a 40–50 % reduction in coronary heart disease incidence among women using these preparations. In contrast, the Women’s Health Initiative clinical trial of estrogen plus progestin found an elevated incidence over a 5.6-year intervention period through July 7, 2002. Toward explaining this discrepancy, the authors analyzed data from this trial, which included 16,608 postmeno-pausal women aged 50–79 years, and corresponding data from 53,054 women in the Women’s Health Initiative observational study, 33 % of whom were estrogen-plus-progestin users at baseline. Estrogen-plus-progestin haz-ard ratio estimates for coronary heart disease, stroke, and venous thromboembolism in the observational study were 39–48 % lower than those in the clinical trial following age adjustment. However, hazard ratios tended to decrease with increasing time from initiation of estrogen-plus-progestin use, and observational study hazard rati