11. A new drug with in vitro activity against HIV is tested on a population of patients with Western-blot confirmed HIV infections. Out of the 200 individuals in the patient population, 100 are chosen by lottery to receive the drug. The drug, which is tasteless, is administered in a cup of orange juice; the other patients receive pure orange juice. Neither the nurses, doctors, nor the patients know which patients receive the drug. At the end of the study period, the number of CD4+ T cells is determined for all of the subjects. This is an example of a

a. Case-control study

b. Case report

c. Cohort study

d. Cross-sectional study

e. Double-blind randomized clinical trial

12. A city has a population of 250,000. Of these, 10,000 have disease X, which is incurable. There are 1,000 new cases and 400 deaths each year from this disease. There are 2,500 deaths per year from all causes. The prevalence of this disease is given by

a. 400/250,000

b. 600/250,000

c. 1,000/250,000 d. 2,500/250,000 e. 10,000/250,000

13. There were no new cases of Ebola virus in the United States from January 1, 1997 through January 1, 1998. Which of the following epidemiologic terms does this statement describe?

a. Incidence

b. Lifetime expectancy

c. Lifetime prevalence

d. Period prevalence

e. Point prevalence

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