Question

identify which of these designs is most appropriate for the given experiment: completely randomized design, randomized block design, or matched pairs design. currently, there is no approved vaccine for the prevention of infection by west nile virus. a clinical trial of a possible vaccine is being planned to include subjects treated with the vaccine while other subjects are given a placebo. the most appropriate design is dropdown design. options: completely randomized, matched pairs, randomized block.

Explanation:

In a clinical trial for a vaccine (with subjects either getting the vaccine or a placebo), a completely randomized design is appropriate when we randomly assign subjects to treatment (vaccine) or control (placebo) groups without blocking or matching, which fits the described scenario here. Matched pairs would require pairing similar subjects, and randomized block would require grouping (blocking) by a factor, but there's no indication of such grouping or pairing here. So the most appropriate is completely randomized.

Answer:

completely randomized