Malaria is a disease spread by mosquitos. Researchers want to test a potential vaccine for the disease, so they plan on recruiting thousands of subjects from each of the 10 countries that are most affected by the disease. The researchers want to use a randomized block design where some subjevrw receive the vaccine and the rest receive a placebo. How should the researchers from the blocks?
Choose 1
A) Each subject should be randomly assigned to a block.
B) Both the subjects and researchers should be kept blind as to which block the subjects are in.
C) Each block should consist of subjects who like in the same country.
D) Subjects in one block should get the vaccine, while subjects in the other block should get the placebo.
E) Each block should consist of subjects who live in different countries.