Epidemiology for Public Health Practice 5th Edition by Robert Friis,Thomas Sellers

تمرين 8

Epidemiologic studies of the role of a suspected factor in the etiology of a disease may be observational or experimental. The essential difference between experimental and observational studies is that in experimental studies: (Choose one answer.)a. The study and control groups are equal in size.
b. The study is prospective.
c. The study and control groups are always comparable with respect to all factors other than the exposure.
d. The investigator determines who shall be exposed to the suspected factor and who shall not.
e. Controls are used.