Which of the following is an example of an epidemiological experiment?
a. To test the effectiveness of a drug, researchers administer it to an experimental group of subjects but not to a control group of subjects.
b. Researchers look at the pattern of cancer development across populations in New England.
c. Researchers conduct a clinical trial to determine whether a treatment for multiple sclerosis is effective.
d. Researchers conduct a double-blind study to determine whether fish oil supplements reduce the frequency of heart attacks.