A study published in the New England Journal of Medicine compared two medicines to treat head lice: an oral medication called ivermectin and a topical lotion containing malathion. Researchers
studied people in 376 households in seven areas around the world. Of the 185 households randomly
assigned to ivermectin, 171 were free from head lice after 2 weeks compared with only 151 of the 191
households randomly assigned to malathion.
(a) Why was it important to randomly assign the treatments (ivermectin/malathion) in this experiment?