Several large observational studies suggested that women who take hormones such

Question

Several large observational studies suggested that women who take hormones such as estrogen after menopause have lower risk of a heart attack than women who do not take hormones. Hormone replacement became popular. But in 2002, several careful experiments showed that hormone replacement does not reduce heart attacks. The National Institutes of Health, after reviewing the evidence, concluded that the observational studies were wrong. Taking hormones after menopause quickly fell out of favor.
(a) Explain the difference between an observational study and an experiment to compare women who do and don’t take hormones after menopause.
(b) Suggest some characteristics of women who choose to take hormones that might affect the rate of heart attacks. In an observational study, these characteristics are confounded with taking hormones.

Explanation / Answer

a) Since this is an observational study, it is essentially anecdotal evidence. Confounding variables are not being controlled or blocked, and because we aren't making sure that all the people are as similar as possible there could be an outside factor unrelated to hormones after menopause. In an experiment, the people in the study would be randomly selected. See b) for an example. b) For example, women who take hormones after menopause may be health buffs that take every possible precaution to be in good health. Because they are so involved in their health, they tend to exercise a lot and take hormones to help their body. Their exercise, not their hormone use, may explain the lower risk of heart attack.

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