Letters to the Editor RE: ‘‘COMBINED POSTMENOPAUSAL HORMONE THERAPY AND CARDIOVASCULAR DISEASE: TOWARD RESOLVING THE DISCREPANCY BETWEEN OBSERVATIONAL STUDIES AND THE WOMEN’S HEALTH INITIATIVE CLINICAL TRIAL’’

We appreciate the effort by Prentice et al. (1) to elucidate the basis for differences in the relation of postmenopausal hormone therapy to risk of coronary heart disease in obser-vational studies and in the Women’s Health Initiative (WHI) trial. Three findings from this and earlier WHI reports (2–4) are key. First, the duration of time since starting hormone therapy differed greatly between the types of studies, in part because the observational studies enrolled a cross-section of post-menopausal women that included many who had already been using hormone therapy for years. Second, differences in time since menopause at hormone therapy initiation were also extreme because women were randomized up to the age of 79 years in the WHI trial, whereas in usual practice hormone therapy is started nea