In the hormone replacement studies of menopausal women, doctors rejected the results of the observational study after conducting the experiment. In the experiment they controlled the effects of confounding variables that had probably influenced the results in the observational study.
In the experiment the doctors used random assignment to treatment groups, a placebo, and double blinding to control the effects of confounding variables.
1. Which of the following are potential confounding variables?
Check all that apply.
A. whether a woman took hormones
B. whether a woman in the study had a heart attack
C. wealth
D. access to health care