Why Were the WHI Results So Unexpected?
Before WHI, several studies had suggested that hormone therapy would reduce the risk of heart disease.[8] Most of these studies, however, were “observational.” In an observational study, scientists do not control the medications that women take. Rather, they observe what happens to women after the women themselves decide whether or not to take hormones. A limitation of this type of study is that the women who decide to take hormones are likely to be different from women who do not take hormones, and these differences may affect the study results. Researchers attempt to account for differences between groups when they analyze the data, but some differences may be difficult to identify or measure. In a clinical trial such as the WHI, researchers assign study subjects to a particular treatment group. Clinical trials generally offer the most convincing evidence about the effects of a treatment, but they’re very expensive. In addition, they are only ethical when there is some initial eviden
