Hormone Replacement Therapy
When women go through menopause, the production of hormones in their bodies changes. The hormonal changes can cause a variety of symptoms that may be reduced by hormone replacement therapy. In the 1980s, hormone replacement therapy was common in the United States.
In the early 1990s, observational studies suggested that hormone replacement therapy had additional benefits, including a reduction in the risk of heart disease. In these observational studies, researchers compared women who took hormones to those who did not take hormones. Health records showed that women taking hormones after menopause had a lower incidence of heart disease. But women who take hormones are different from other women. They tend to be richer and more educated, to have better nutrition, and to visit the doctor more frequently. These women have many habits and advantages that contribute to good health, so it is not surprising that they have fewer heart attacks. But can we conclude from these studies that the hormones caused the reduction in heart attacks? No. The results are confounded by the influence of these other factors.
In 2002, the Women's Health Initiative sponsored a large-scale, well-designed experiment to study the health implications of hormone replacement therapy. In this experiment, researchers randomly assigned over 16,000 women to one of two treatments. One group took hormones. The other group took a placebo. A placebo is a pill with no active ingredients that looks like the hormone pill. The experiment was double-blind. Blind means that women did not know if they were receiving hormones or the placebo. Double-blind means that the information was coded, so researchers administering the pills did not know which treatment the women received. After 5 years, the group taking hormones had a higher incidence of heart disease and breast cancer. This is exactly the opposite result from the result found in the observational studies! In fact, the differences were so significant that the researchers ended the experiment early. The National Institutes of Health declared that the observational studies were wrong. Hormone replacement therapy to treat menopausal symptoms is now rarely used.
Recall the hormone replacement studies you just read about.
- Identify the explanatory variable and the response variable in the hormone replacement studies.
- What are some of the factors that may be confounding variables in the observational study?
- How did the experiment control for the effects of the confounding variables you identified?