In the 1954 clinical trial of the Salk polio vaccine, many different study designs were considered. Discuss the advantages and disadvantages of each of the following designs:

(a) Select a random sample of children and vaccinate them. Compare their polio rates to children in the US.

(b) Vaccinate children whose parents have volunteered them for the study and then compare the polio rate for vaccinated children with the rate for unvaccinated children in the same area.

(c) Vaccinate children in one city and compare their polio rate to children in another city.