Do blood-building drugs help brain development in babies born prematurely? Researchers randomly assigned 53 babies, born more than a month premature and weighing less than 3 pounds, to one of three groups. Babies either received injections of erythropoietin (EPO) three times a week, darbepoetin once a week for several weeks, or no treatment. Results? Babies who got the medicines scored much better by age 4 on measures of intelligence, language, and memory than the babies who received no treatment.

a. Explain how this experiment used comparison.

b. Explain the purpose of randomly assigning the babies to the three treatments.

c. Name two variables that were controlled in this experiment and why it was beneficial to control these variables.

d. Explain how this experiment used replication. What is the purpose of replication in this context?